Magnetic recording medium with high thermal stability, method for producing the same, and magnetic recording apparatus

ABSTRACT

A magnetic recording medium comprises an information-recording film and a ferromagnetic film on a substrate. The information-recording film is composed of, for example, an amorphous ferrimagnetic material having perpendicular magnetization. Further, the ferromagnetic film is composed of a magnetic material which has saturation magnetization larger than that of the information-recording film. Accordingly, the leak magnetic flux from the ferromagnetic film is larger than that from the information-recording film. The magnetic recording medium and a magnetic recording apparatus are obtained, which are excellent in thermal stability and which are preferred to perform super high density recording.

TECHNICAL FIELD

The present invention relates to a magnetic recording medium formagnetically recording information thereon, and a magnetic recordingapparatus provided with the same. In particular, the present inventionrelates to a magnetic recording medium which is excellent in thermalstability and which has high performance and high reliability. Thepresent invention also relates to a magnetic recording apparatusprovided with the same.

BACKGROUND ART

Recent development of advanced information society is remarkable. Themultimedia, in which pieces of information in a variety of forms areintegrated, rapidly comes into widespread use. A magnetic diskapparatus, which is installed to a computer or the like, is known as oneof the multimedia. At present, development is advanced for the magneticdisk apparatus aiming at the miniaturization while improving therecording density. Concurrently therewith, development is also advancedquickly in order to realize a low price of the apparatus.

In order to realize the high density on the magnetic disk, for example,it is demanded that (1) the distance between the disk and the magnetichead is narrowed, (2) the coercivity of the magnetic recording medium isincreased, (3) the signal-processing method is executed at a high speed,and (4) the thermal fluctuation of the magnetic recording medium isreduced.

In order to realize the high density magnetic recording on the magneticrecording medium, it is necessary to increase the coercivity of themagnetic film. A material based on the Co—Cr—Pt(—Ta) system has beenwidely used for the magnetic film of the magnetic recording medium. Thismaterial is a crystalline material in which crystal grains of Co ofabout 20 nm are deposited. In order to realize, for example, an a realrecording density exceeding 40 Gbits/inch² on the magnetic recordingmedium in which such a material is used for the magnetic film, it isnecessary to further decrease the size of the unit (magnetic cluster) inwhich the inversion of magnetization occurs during recording or erasure,and it is necessary to decrease the grain size distribution so that thestructure and the organization of the magnetic film are preciselycontrolled. When the control is made as described above, the noise,which is generated from the medium during the reproduction, can bereduced. However, any dispersion arises in the crystal grain size.Especially, when grains having small sizes exist in the magnetic film,then the thermal demagnetization and the thermal fluctuation take place,and the magnetic domain, which is formed in the magnetic film, fails tostably exist in some cases. Especially, when the magnetic domain is madefine and minute as the recording density is increased, remarkableinfluences are exerted by the thermal demagnetization and the thermalfluctuation. In order to reduce the noise generated from the medium bymaking the crystal grains to be fine and minute, the thermal fluctuationis suddenly increased. Especially, when the crystal grain diameter isnot more than 10 nm to 8 nm, the thermal fluctuation has appearedconspicuously. For this reason, in view of the reduction of the thermaldemagnetization and the thermal fluctuation, it becomes an importanttechnique to control the crystal grain size distribution. As a methodfor realizing the above, for example, U.S. Pat. No. 4,652,499 disclosesa method in which a seed film is provided between a substrate and amagnetic film.

However, the magnetic disk, which uses a ferromagnetic film as amagnetic film, has involved a certain limit of control of the magneticgrain diameter and the distribution thereof in the magnetic film byusing the method in which the seed film is provided as described above.For example, when the super high density recording exceeding 40Gbits/inch² is performed, the grain diameter distribution has been broadwith large-sized grains and minute grains existing in a mixed manner,for example, even when the material for the seed film, the filmformation condition, and the structure of the seed film are adjusted.When information is recorded (when magnetization is inverted), theminute grains are affected by influences of leak magnetic field fromsurrounding magnetic grains. On the other hand, the large-sized grainsinteract with surrounding magnetic grains. Further, some magneticgrains, which have grain diameters larger than the average of those ofthe magnetic grains, cause the increase in noise whenrecording/reproduction is performed. Other magnetic grains, which havegrain diameters smaller than the average, sometimes increase the thermalfluctuation when recording/reproduction is performed. For this reason,it has been difficult to reliably record information. As a result of thepresence of magnetic grains having a variety of sizes in a mixed mannerin the mass of magnetic grains, the boundary line between an area inwhich inversion of magnetization occurs and an area in which inversionof magnetization does not occur exhibits a rough zigzag pattern as awhole. Such a phenomenon also causes the increase in noise.

In order to perform the high density recording, it is also importantthat the magnetic layer is thermally stable. The value represented by(Ku·V)/(k·T) can be used as an index for the thermal stability of themagnetic layer. In the expression, Ku represents the magnetic anisotropyenergy, V represents the volume of activation, k represents theBoltzmann's constant, and T represents the temperature. As the value isincreased, the magnetic layer is thermally stable. Therefore, in orderto enhance the thermal stability of the magnetic layer, it is necessaryto increase the volume of activation V and the magnetic anisotropyenergy Ku. This fact also holds in the same manner as described abovefor the magnetic film for perpendicular magnetic recording based on theCo—Cr system.

In the case of the crystalline material based on the Co system, when themagnetic grains are made fine and minute, it is anticipated that themagnetization possessed by the magnetic-crystal grains may be changed,because of transfer into the mesoscopic region. As a result, it isfurther difficult to secure the heat resistance of the magnetic film.

In order to satisfy the requirement as described above, it has beeninvestigated that an amorphous alloy as a ferrimagnetic substance, whichis composed of rare earth element and iron family element, is used for amagnetic film for recording information. For example, it has beenreported in 23rd Annual Meeting of Magnetic Society of Japan (8aB11,1999) that a rare earth-iron family alloy as an amorphous material ishopeful as a magnetic material which is excellent in thermal stabilityand which is preferred for high density recording. In “InterMag 2000HA-04”, a medium, in which an amorphous alloy based on the rareearth-iron family is used for a recording film, is disclosed as amagnetic recording medium which is resistant to the thermal fluctuation.Although such an amorphous alloy is excellent in thermal stability, themagnetic wall is liable to move. Therefore, when a magnetic field isapplied during the recording of information to record the information,it has been difficult to stably form the minute magnetic domain in amagnetic layer. For this reason, it has been necessary that the magneticwall position (corresponding to the information bit position) isdetermined highly accurately so that the position of the magnetic domainmay be correctly established during the recording of information. Thisinconvenience results from the fact that the rare earth-transition metalalloy is a magnetic material of the magnetic wall movement type.

The present invention has been made taking the foregoing situations intoconsideration. A first object of the present invention is to provide amagnetic recording medium which has a large volume of activation of amagnetic film, which has high thermal stability, and which is excellentin reproduction performance, and a magnetic recording apparatus providedwith the same.

A second object of the present invention is to provide a low noisemagnetic recording medium in which the shape of the magnetic domainhardly takes a form of zigzag pattern in a magnetization transition areaand the zigzag pattern is not reflected, and a magnetic recordingapparatus provided with the same.

A third object of the present invention is to provide a magneticrecording medium which has large magnetic anisotropy, which is excellentin stability of recorded information, and which makes it possible toreliably form the minute magnetic domain, and a magnetic recordingapparatus provided with the same.

A fourth object of the present invention is to provide a magneticrecording medium which has a simplified stacked (laminated) structureand which is suitable for mass production, and a magnetic recordingapparatus provided with the same.

A fifth object of the present invention is to provide a magneticrecording medium which makes it possible to highly accurately determinethe position of the magnetic wall (i.e., the position of the magneticdomain) formed in an amorphous magnetic film during recording ofinformation, and a magnetic recording apparatus provided with the same.

A sixth object of the present invention is to provide a magneticrecording medium which is preferred for the super high density recordingexceeding 40 Gbits/inch² (6.20 Gbits/cm²), and a magnetic recordingapparatus provided with the same.

DISCLOSURE OF THE INVENTION

According to a first aspect of the present invention, there is provideda magnetic recording medium for reproducing information thereon by usinga magnetic head, the magnetic recording medium comprising:

-   -   a substrate;    -   an amorphous magnetic film in which information is recorded; and    -   a ferromagnetic film.

The magnetic recording medium according to the first aspect of thepresent invention is provided with the amorphous magnetic film which iscomposed of an amorphous magnetic material. Information is recorded inthe amorphous magnetic film. The amorphous magnetic film may beconstructed, for example, with a ferrimagnetic material which has aneasy axis of magnetization in a direction perpendicular to a substratesurface. Such an amorphous magnetic film is resistant to the thermalfluctuation owing to the amorphous structure in which no crystal grainboundary exists. Further, such an amorphous magnetic film has largeanisotropy, because it is composed of the ferrimagnetic material.Therefore, fine and minute magnetic domains can be formed in themagnetic recording medium of the present invention which is providedwith the amorphous magnetic film as a recording layer for recordinginformation therein. Accordingly, information can be recorded at a highdensity, and the magnetic recording medium of the present invention isexcellent in thermal stability as well. The information, which isrecorded in the amorphous magnetic film, can be reproduced by using amagnetic head.

In the magnetic recording medium according to the first aspect of thepresent invention, the ferromagnetic film may be formed on a side closeto the magnetic head in contact with the amorphous magnetic film. Forexample, when information is recorded and reproduced with the magnetichead arranged on a side opposite to the substrate, a structure may beadopted, in which the amorphous magnetic film and the ferromagnetic filmare formed in this order on the substrate. In this arrangement, it ispreferable that the ferromagnetic film has an easy axis of magnetizationin a direction perpendicular to a substrate surface, and theferromagnetic film has saturation magnetization which is larger thansaturation magnetization of the amorphous magnetic film. When theferromagnetic film is provided in contact with the amorphous magneticfilm, the amorphous magnetic film and the ferromagnetic film aremagnetically coupled to one another. When information is reproduced, themagnetization of the amorphous magnetic film is magnetically transferredto the ferromagnetic film. Therefore, when the magnitude of the magneticflux from the ferromagnetic film or the amount of change of the magneticflux is detected by using the reproducing magnetic head duringreproduction of information, the information, which is recorded in theamorphous magnetic film, can be reproduced at a large reproduced signalintensity. As described above, the ferromagnetic film functions as areproducing layer which makes it possible to substantially amplify themagnetic flux generated from the amorphous magnetic film.

It is preferable for such a ferromagnetic film to use a magnetic thinfilm principally containing oxide of Co or alloy principally containingCo. At least one element selected from of Cr, Pt, Pd, Ta, Nb, Si, and Timay be contained in the above. The ferromagnetic film, which is composedthe material as described above, also makes it possible to prevent theamorphous magnetic film from rust and corrosion.

The ferromagnetic film can be also constructed with a material which hassmall perpendicular magnetic anisotropy in a state of single layer andwhich does not form any perpendicularly magnetizable film. In this case,the perpendicular magnetic anisotropy may be induced by magneticallycoupling the ferromagnetic film and the information-recording film.

In the magnetic recording medium according to the first aspect of thepresent invention, it is preferable that the material for constructingthe amorphous magnetic film is a rare earth-transition metal (ironfamily element) material. As for the rare earth-transition metalmaterial, the rare earth element is preferably at least one of Tb, Gd,Dy, and Ho, and the transition metal is preferably at least one of Fe,Co, and Ni.

In the present invention, the term “amorphous” means the structure inwhich atoms are irregularly arranged, and the term means, for example,the structure in which no diffraction peak based on the crystalstructure is observed when the X-ray diffraction analysis is performed.

The term “amorphous magnetic film” means the magnetic film which iscomposed of the “amorphous” magnetic material, and the term resides inthe concept which includes the alternately stacked film constructed byalternately stacking amorphous magnetic layers, and the artificiallattice film composed of the amorphous magnetic material. For example,the artificial lattice film composed of the amorphous magnetic materialmay have such a structure that one or more amorphous thin films composedof iron family element and one or more amorphous thin films composed ofrare earth element are alternately stacked to provide a periodic featuresimilar to that of crystals in the direction of film thickness. Theartificial lattice film may include not only the multilayered film(alternately stacked multilayered film) having the structure in whichlayers composed of different substances are alternately stacked in thefilm thickness direction, but also the artificial lattice film havingthe structure in which areas of different substances periodically appearin a specified pattern in the film surface direction. When the amorphousmagnetic film is constructed by using the artificial lattice film asdescribed above, the obtained film is more resistant to the thermalfluctuation as compared with a case in which an amorphous magnetic filmis constructed in a single layer state by using the same magneticmaterial as that of the artificial lattice film. Further, when theamorphous magnetic film is constructed by using the artificial latticefilm, the anisotropy is successfully increased as compared with a casein which an amorphous magnetic film is constructed with an alloy thinfilm of a ferrimagnetic material. Therefore, such an amorphous magneticfilm is excellent in thermal stability, which is extremely preferred toperform the high density recording.

When the amorphous magnetic film is constructed with the artificiallattice film composed of the iron family element and the rare earthelement, then the iron family element is preferably at least one elementselected from Fe, Co, and Ni, and the rare earth element is preferablyat least one element selected from Tb, Gd, Dy, and Ho. A two-layeredfilm, which is composed of at least two elements selected from Fe, Co,and Ni, may be used for the thin film composed of the iron familyelement. Alternatively, the thin film, which is composed of the ironfamily element, may be formed with an alloy thin film composed of atleast two elements selected from Fe, Co, and Ni in the artificiallattice film. Further, the artificial lattice film is preferablyconstructed so that the directions of the sub-lattice magnetization ofthe thin film composed of the iron family element and the sub-latticemagnetization of the thin film composed of the rare earth element areantiparallel. It is most preferable that the sub-lattice magnetizationof the iron family element is more dominant than the sub-latticemagnetization of the rare earth element so as to increase the saturationmagnetization which contributes to the magnitude of the reproducedsignal output.

In the magnetic recording medium according to the first aspect of thepresent invention, the ferromagnetic film also has an effect (pinningeffect) to suppress the movement of the magnetic wall of the recordingmagnetic domain formed in the amorphous magnetic film.

The magnetic recording medium according to the first aspect of thepresent invention may further comprise a magnetic wall movement controllayer (pinning layer) which suppresses the movement of the magnetic wallof the recording magnetic domain formed in the amorphous magnetic film.That is, the magnetic recording medium may comprise an amorphousmagnetic film for recording information, a ferromagnetic film forsubstantially increasing a magnetic flux generated from the amorphousmagnetic film, and a magnetic wall movement control layer forcontrolling movement of a magnetic wall of a recording magnetic domainformed in the amorphous magnetic film. When a magnetic material of themagnetic wall movement type is used for the amorphous magnetic film, theposition of the magnetic wall formed by recording information is hardlysettled. In order to avoid such an inconvenience, it is preferable thata material of the magnetization rotation type is used for the magneticwall movement control layer. As described above, it is especiallypreferable that the material of the magnetic wall movement type is usedfor the amorphous magnetic film, and the material of the magnetizationrotation type is used for the magnetic wall movement control layer.

In the present invention, the magnetic wall movement control layer canbe provided at an arbitrary position in the magnetic recording medium.However, it is preferable that the magnetic wall movement control layeris formed so that the amorphous magnetic film is positioned between themagnetic wall movement control layer and the ferromagnetic film. It isdesirable that the layers are stacked so that the ferromagnetic film ispositioned on the side close to the magnetic head for reproducinginformation, and the magnetic wall movement control layer is positionedon the side far from the magnetic head. It is preferable that all of theeasy axes of magnetization of the amorphous magnetic film, theferromagnetic film, and the magnetic wall movement control layer are inthe same direction in a state in which the respective layers constitutethe magnetic recording medium.

In the present invention, it is preferable that the amorphous magneticfilm, the ferromagnetic film, and the magnetic wall movement controllayer are constructed so that the coercivity of the amorphous magneticfilm is largest when the coercivities possessed by the respective layersare compared with each other.

It is preferable that the ferromagnetic film has the largest saturationmagnetization when the saturation magnetizations possessed by therespective layers of the amorphous magnetic film, the ferromagneticfilm, and the magnetic wall movement control layer are compared witheach other. Accordingly, the information, which is recorded in theamorphous magnetic film, can be reproduced with larger reproduced signalintensity.

It is preferable that the magnetic wall movement control layer iscomposed of a magnetic material of the magnetization rotation type. Forexample, it is preferable that the magnetic wall movement control layeris composed of an alloy which principally contains Co, oxide of Co, orCo—Cr alloy and which further contains at least one element selectedfrom Pt, Pd, Ta, Nb, and Ti. When the magnetic wall movement controllayer is constructed by using the material as described above, it ispossible to highly accurately establish the position of the magneticwall of the recording magnetic domain formed in the amorphous magneticfilm. Further, the size and the shape of the recording magnetic domaincan be made to be a desired size and a desired shape. Accordingly,information can be recorded at a super high density in the amorphousmagnetic film, and the recorded information can be reproduced at lownoise.

In the magnetic recording medium according to the first aspect of thepresent invention, in view of the high density recording, as for themagnetic anisotropy possessed by the amorphous magnetic film, theperpendicular magnetic anisotropy energy in the direction perpendicularto the substrate surface is preferably not less than 3×10⁶ erg/cm³ (0.3J/cm³), and especially preferably not less than 6×10⁶ erg/cm³ (0.6J/cm³).

It is preferable that the material for constructing the amorphousmagnetic film has such magnetic characteristics that the saturationmagnetization is not less than 100 emu/cm³, and the coercivity is notless than 3 kOe (about 238.74 kA/m). Further, it is preferable that thefilm thickness is not more than 100 nm. The values of the saturationmagnetization and the coercivity of the amorphous magnetic film can becontrolled by changing the composition of the material for constructingthe same. Accordingly, it is possible to provide the magnetic recordingmedium having magnetic characteristics in conformity with thecharacteristics of the magnetic head of the magnetic recordingapparatus.

In the present invention, in order to enhance the thermal stability ofthe amorphous magnetic film, it is preferable to select the material forconstructing the amorphous magnetic film so that the volume ofactivation V in the amorphous magnetic film is substantially equal tothe volume of one magnetic domain formed in the amorphous magnetic film,concerning the relationship represented by KuV/kT (Ku: magneticanisotropy constant, V: volume of activation, k: Boltzmann's constant,T: temperature). As for such a material, for example, Tb—Fe—Co,Tb—Dy—Fe—Co, Tb—Gd—Fe—Co, Gd—Dy—Fe—Co, Gd—Ho—Fe—Co, Dy—Ho—Fe—Co,Ho—Fe—Co, and Dy—Fe—Co are preferred. When the amorphous magnetic filmis constructed as the artificial lattice film, it is preferable to usean alternately stacked film of rare earth element, Fe, and Co, analternately stacked film of rare earth element and FeCo alloy,especially a Tb/Fe/Co film.

In the present invention, the ferromagnetic film can be constructed witha magnetic thin film principally containing oxide of Co or alloyprincipally containing Co, in which at least one element of Cr, Pt, Pd,Ta, Nb, Si, and Ti may be contained. Alternatively, the ferromagneticfilm may be constructed with an alternately stacked multilayered filmobtained by alternately stacking at least one element of Co, Ni, and Feand at least one element of Pt, Pd, and Rh. Further alternatively, theferromagnetic film may be constructed with an alternately stackedmultilayered film obtained by alternately stacking one or more alloylayers composed of at least one element of Co, Ni, and Fe and at leastone element of Pt, Pd, and Rh, and one or more layers composed of atleast one element of Pt, Pd, and Rh.

According to a second aspect of the present invention, there is provideda magnetic recording medium comprising:

-   -   a substrate and a magnetic film in which information is        recorded, wherein:    -   the magnetic film is an amorphous film which contains at least        one element of oxygen and nitrogen.

The magnetic recording medium of the present invention contains at leastone of oxygen and nitrogen not at an impurity level but in a significantamount in the magnetic film having the amorphous structure for recordinginformation. The significant amount of oxygen or nitrogen, which iscontained in the magnetic film, exists in a dispersed manner in themagnetic film as a simple substance or as a compound (oxide or nitride)with the material for constructing the magnetic film. The magneticproperty of the simple substance or the compound of oxygen or nitrogenin the magnetic film is weakened, or the magnetic property disappears.Therefore, it is possible to effectively avoid the movement of themagnetic wall formed in the magnetic film.

Conventionally, when the magnetic domain is formed in the magnetic filmof the magnetic wall movement type such as the amorphous film, themagnetic wall, which is formed by the adjoining magnetic domains, iseasily moved in the in-plane direction as schematically shown in FIG.10(B). Therefore, the edge position of the recorded magnetic domain hasbeen fluctuated. For this reason, it has been difficult to highlyaccurately determine the shape and the position of the magnetic domainformed in the magnetic film. In the present invention, as shown in FIG.10(A), the compound or the simple substance of oxygen or nitrogen isdispersed as foreign matters in the magnetic film, and the area, inwhich the compound or simple substance exists, forms the pinning siterespectively. When the magnetic domains are formed in such a magneticfilm, the pinning sites in the magnetic film obstruct the movement ofthe magnetic wall. Therefore, the magnetic domain, which is recorded inthe magnetic film, is correctly formed at a desired position with adesired shape without causing any fluctuation.

In the present invention, for example, according to the result ofanalysis by ESCA (Electron Spectroscopy for Chemical Analysis) or AES(Auger Electron Spectroscopy), the content of at least one of oxygen andnitrogen in the magnetic film is at least not less than 1 at %, andpreferably 1 at % to 20 at %, in order to allow oxygen or nitrogen toeffectively function as the pinning site in the magnetic film.

In the present invention, for example, the magnetic film may compriseone or more layers each of which contains a significant amount of oxygenor nitrogen, and one or more layers each of which substantially containsneither oxygen nor nitrogen. The magnetic film may have a structure inwhich the layers are periodically stacked. In the layer containingoxygen or nitrogen, it is especially preferable that areas containingoxygen or nitrogen are dispersed in an island form in the plane when thelayer is observed in a plan view. However, such areas may be formed overthe entire surface. It is preferable that the layer, which substantiallycontains neither oxygen nor nitrogen, has a film thickness of not lessthan 3 nm and not more than 10 nm. It is preferable that the layer,which contains oxygen or nitrogen, has a film thickness of not less than0.05 nm and not more than 0.5 nm.

In the magnetic recording medium according to the second aspect of thepresent invention, a ferrimagnetic material, which is composed of, forexample, a rare earth element and an iron family element, can be usedfor the amorphous magnetic film. When the magnetic film is constructedas a perpendicularly magnetizable film, for example, the rare earthelement is preferably at least one element selected from Gd, Tb, Dy, andHo, and the iron family element is preferably at least one elementselected from Fe, Co, and Ni. When the magnetic film is constructed asan in-plane magnetizable film, for example, the rare earth element ispreferably at least one element selected from Er, La, Ce, Pr, Nd, Pm,Sm, Eu, Tm, Yb, Lu, and Y, and the iron family element is preferably atleast one element selected from Fe, Co, and Ni. When the magnetic filmis constructed as described above, it is preferable that oxygen ornitrogen, which is contained in the magnetic film, is coupled to therare earth element.

In the magnetic recording medium according to the second aspect of thepresent invention, the magnetic film may be constructed with theartificial lattice film described above. The artificial lattice film mayhave a structure in which one or more thin films each composed of a rareearth element and one or more thin films each composed of an iron familyelement are alternately stacked. For example, the rare earth element ispreferably at least one element selected from Gd, Tb, Dy, and Ho, andthe iron family element is preferably at least one element selected fromFe, Co, and Ni. When the magnetic film is constructed as describedabove, it is preferable that oxygen or nitrogen is contained in the thinfilm composed of the iron family element, and most preferably in a layerof Co of the iron family element, for the following reason. That is, Cohas the strongest magnetic interaction among the iron family elements.When oxygen or nitrogen is added to Co, it is possible to exhibitnon-magnetic properties. As a result, innumerable non-magnetic areas arestudded in the magnetic film, and it is possible to decrease theexchange coupling force. Accordingly, it is possible to form extremelyminute magnetic domains in the magnetic film, and thus it is possible torealize the high density recording.

The artificial lattice film may be also an artificial lattice film(alternately stacked multilayered film) in which one or more thin filmseach composed of a platinum group element and one or more thin filmseach composed of an iron family element are alternately stacked. Theplatinum group element is preferably at least one element selected fromPt, Pd, and Rh, and the iron family element is preferably at least oneelement selected from Fe, Co, and Ni. Also in this case, it ispreferable to contain oxygen or nitrogen in the layer composed of theiron family element of the layers for constructing the artificiallattice film. Especially, it is most preferable to contain oxygen ornitrogen in the layer composed of Co.

In the second aspect of the present invention, it is preferable that themagnetic film has such perpendicular magnetic anisotropy that an easyaxis of magnetization is directed in a direction perpendicular to asubstrate surface.

According to a third aspect of the present invention, there is provideda method for producing a magnetic recording medium, comprising:

-   -   providing a substrate; and    -   forming an amorphous magnetic film on the substrate by means of        sputtering, wherein:    -   the sputtering is performed in an atmosphere in which at least        one of oxygen and nitrogen is contained in an inert gas.

According to the production method of the third aspect of the presentinvention, at least one of oxygen and nitrogen can be contained in asignificant amount in the magnetic film. Therefore, the productionmethod is extremely preferred as a method for producing the magneticrecording medium according to the second aspect of the presentinvention.

In the production method according to the third aspect of the presentinvention, it is preferable that at least one of oxygen and nitrogen iscontained at a concentration of 0.1% by volume to 20% by volume in thesputtering gas atmosphere when the sputtering is performed.

In the production method of the present invention, oxygen or nitrogencan be consequently contained in the sputtering gas atmosphere as wellby intentionally lowering the degree of vacuum in a sputtering filmformation chamber as compared with the normal operation.

In the production method according to the third aspect of the presentinvention, oxygen or nitrogen is contained when the sputtering isperformed. For this reason, when any material, which tends to react withoxygen or nitrogen, is present in the material for constructing thetarget, it is feared that a magnetic film having a desired compositioncannot be formed. Therefore, it is desirable that the target material isconstructed after previously adjusting the composition ratio of thematerial which reacts with oxygen or nitrogen.

According to a fourth aspect of the present invention, there is provideda method for producing a magnetic recording medium, comprising:

-   -   providing a substrate; and    -   forming an amorphous magnetic film on the substrate by means of        sputtering, wherein:    -   the sputtering comprises such operation that the sputtering is        temporality interrupted and then the sputtering is resumed.

In the production method according to the fourth aspect of the presentinvention, the sputtering operation is temporarily stopped when themagnetic film is formed as a film. Accordingly, the surface of theformed magnetic film is naturally oxidized or naturally nitrided withoxygen or nitrogen which is contained as an impurity in the inert gasatmosphere. Further, a structure is obtained, in which one or morelayers each containing oxygen or nitrogen in a significant amount andone or more layers each substantially containing neither oxygen nornitrogen are alternately stacked, by repeatedly performing in aplurality of times the operation to perform the sputtering and theoperation to temporarily stop the sputtering. Therefore, the productionmethod according to the fourth aspect of the present invention isextremely preferred as a method for producing the magnetic recordingmedium according to the second aspect of the present invention.

According to a fifth aspect of the present invention, there is provideda magnetic recording medium comprising:

-   -   an information-recording film which is provided on a substrate        and which has such a structure that one or more magnetic films        and one or more non-magnetic films are alternately stacked,        wherein:    -   the non-magnetic film has a film thickness of not more than 1        nm.

The magnetic recording medium according to the fifth aspect of thepresent invention comprises the information-recording film having thestructure in which the magnetic film and the non-magnetic film havingthe film thickness of not more than 1 nm are alternately stacked. Thestate, in which “the film thickness of the non-magnetic film is not morethan 1 nm”, includes not only a state in which the non-magnetic film isformed as a continuous film but also a state in which a plurality ofareas each composed of a nonmagnetic material are dispersed in a form ofislands and a state in which a plurality of openings are dispersed in acontinuous film. Usually, when the non-magnetic film is formed in athickness of not more than 1 nm, the cross section of the non-magneticfilm is observed to be substantially layered. However, when the planarstructure is observed, it is appreciated that areas composed of thenon-magnetic material are dispersed in a form of islands on the plane.The island-shaped non-magnetic areas magnetically cut the magnetic filmin the information-recording film into pieces, and thus they function aspinning sites. That is, as shown in a schematic sectional view in FIG.16, the magnetic films, which are positioned over and under the portionB in which the island-shaped non-magnetic area exists, aremagnetostatically coupled by the aid of the non-magnetic area in theportion B. Therefore, the magnetic coupling of the magnetic films isweakened at the portion at which the non-magnetic area exists. On theother hand, the magnetic films are subjected to the exchange coupling atthe portion A at which the non-magnetic area is absent. In this way,innumerable portions having strong magnetic coupling force andinnumerable portions having weak magnetic coupling force are studded inthe information-recording film. Owing to the difference in magneticcoupling force as described above, the magnetic wall, which is formed inthe information-recording film, is prevented from moving in the film.Therefore, it is possible to highly accurately fix the position of therecording magnetic domain in the information-recording film. Thus, it ispossible to reliably form the minute magnetic domain.

The non-magnetic film, which constitutes the information-recording film,functions as the pinning site even in the case of one layer. However, inorder to enhance the pinning effect, it is preferable that thenonmagnetic film is provided in multiple layers. It is preferable thatthe island-shaped area (non-magnetic area) of the non-magnetic materialhas a size of about several nm to 5 nm. Considering, for example, thefilm thickness of each of the films which constitute the magneticrecording medium and the stability of the magnetic head which floatsover the magnetic recording medium, it is most preferable that the areais granular and composed of grains of about 2 to 3 nm.

In the present invention, it is preferable that the film thickness ofthe non-magnetic film of the information-recording film is not less than5% and not more than 20% of the film thickness of the magnetic film.When the film thickness of the non-magnetic film is within the range asdescribed above, it is possible to sufficiently exhibit the pinningeffect for the magnetic wall. It is most preferable that the filmthickness of the non-magnetic film is 0.2 nm to 0.5 nm.

In the present invention, it is preferable that the magnetic film forconstructing the information-recording film is an amorphous film. Forexample, a ferrimagnetic material, which is composed of a rare earthelement and an iron family element, can be used for the amorphous film.When the magnetic film is constructed as a perpendicularly magnetizablefilm, for example, the rare earth element is preferably at least oneelement selected from Gd, Tb, Dy, and Ho, and the iron family element ispreferably at least one element selected from Fe, Co, and Ni. When themagnetic film is constructed as an in-plane magnetizable film, forexample, the rare earth element is preferably at least one elementselected from Er, La, Ce, Pr, Nd, Pm, Sm, Eu, Tm, Yb, Lu, and Y, and theiron family element is at least one element selected from Fe, Co, andNi.

In the magnetic recording medium according to the fifth aspect of thepresent invention, the magnetic film, which constitutes theinformation-recording film, may be formed with the artificial latticefilm as described above. The artificial lattice film may have, forexample, such a structure that one or more layers each composed of arare earth element and one or more layers each composed of an ironfamily element are alternately stacked. For example, the rare earthelement is preferably at least one element selected from Gd, Tb, Dy, andHo, and the iron family element is preferably at least one elementselected from Fe, Co, and Ni.

The magnetic film, which constitutes the information-recording film, maybe also an artificial lattice film (alternately stacked multilayeredfilm) constructed by alternately stacking one or more layers eachcomposed of a platinum group element and one or more layers eachcomposed of an iron family element. The platinum group element ispreferably at least one element selected from Pt, Pd, and Rh, and theiron family element is preferably at least one element selected from Fe,Co, and Ni.

In the present invention, those preferably used for the material forconstructing the non-magnetic film of the information-recording filminclude, for example, at least one element selected from Cr, Nb, Ti, Ta,Si, Al, Pd, Rh, Zr, Re, Mo, W, Ir, V, and Cu, aluminum nitride, siliconnitride, aluminum oxide, and zirconium oxide.

In the present invention, it is preferable that the magnetic film of theinformation-recording film has perpendicular magnetic anisotropy with aneasy axis of magnetization in the direction perpendicular to thesubstrate surface. It is preferable that the magnetic film has astructure in which no diffraction peak based on the crystal structure isobserved when the X-ray diffraction analysis is performed.

In the present invention, the information-recording film can bemanufactured by alternately forming films of a magnetic material and anon-magnetic material by means of, for example, the dry process or thewet process. The film may be formed by means of the dry process or thewet process with a material in which a non-magnetic material isuniformly dispersed in a magnetic material. The information-recordingfilm, which is manufactured by the method as described above, is a filmin which the magnetic films and the non-magnetic films in a state inwhich a plurality of areas composed of the non-magnetic material aredispersed in an island form are stacked substantially alternately. Theinformation-recording film can be also manufactured by alternatelyforming films, i.e., films comprising a non-magnetic material dispersedin an iron family element and films composed of a rare earth element (ora platinum group element).

In the magnetic recording media according to the first, second, andfifth aspects of the present invention, the substrate may be composedof, for example, glass, resin, or Al alloy. It is preferable that thesubstrate has an uneven or concave/convex texture on the surface. Thetexture on the substrate surface serves as the obstacle for the movementof the magnetic wall between magnetic domains when information isrecorded or erased. Therefore, the movement of the magnetic wall, whichwould be otherwise caused by the recording or the erasing of therecording magnetic domain, is suppressed. Thus, it is possible todecrease the noise during the recording and reproduction. Further, theposition on the medium of the magnetic domain formed in the amorphousmagnetic film, the magnetic film, or the information-recording film canbe controlled to be a desired position. Therefore, the arrangement asdescribed above is suitable for the high density recording. Further, byusing the substrate having the texture as described above, it is alsopossible to control the direction of the magnetic anisotropy of theinformation-recording film formed on the substrate. The texture may beconstructed by processing the substrate surface, or the texture may beconstructed by forming a thin film having concave/convex unevenness onthe substrate.

In the magnetic recording media according to the first, second, andfifth aspects of the present invention, it is preferable that the filmfor recording information therein (including the amorphous magneticfilm, the magnetic film, and the information-recording film, hereinafterappropriately referred to as “information-recording film”) exhibits suchmagnetic characteristics that substantially no peak is obtained (i.e.,the value of δM is substantially zero), or a magnetic field intensityobtained when a peak is obtained (magnetic film intensity at which δM ismaximum) is not more than 30% of a coercivity of theinformation-recording film, when δM(H) represented by the followingexpression (1) is plotted with respect to the measured magnetic field Hto obtain a δM curve:δM(H)=Id(H)=[1−2Ir(H)] . . . (1)

In the expression, Id(h) represents the DC demagnetization remanentmagnetization curve (DC demagnetization remanence curve) and Ir(H)represents the isothermal remanent magnetization curve. The DCdemagnetization remanent magnetization curve Id(H) is a curve obtainedsuch that the magnetic field (H) in the direction opposite to thedirection of magnetization is gradually increased and applied to asample having been subjected to saturation magnetization in a certaindirection beforehand, and thus the remanent magnetization with respectto the magnitude of the applied magnetic field is normalized andplotted. The isothermal remanent magnetization curve Ir(H) is a curveobtained such that the magnetic field (H) is gradually increased andapplied to a sample having been subjected to demagnetization beforehand,and thus the remanent magnetization with respect to the magnitude of theapplied magnetic field is normalized and plotted.

It is known that the δM plot, which is obtained on the basis of the DCdemagnetization remanent magnetization curve and the isothermal remanentmagnetization curve, is used for a method for expressing the magneticcoupling force between crystal grains of conventional Co-basedcrystalline materials and granular materials. As for the δM plot, forexample, reference may be made to “K. O'Grady et al., IEEE TRANSACTIONSON MAGNETICS, VOL. 29, NO. 1, JANUARY (1993)”.

The present inventors have considered that atoms or molecules, whichconstitute the amorphous material, construct minute aggregates not onlyin the crystalline material but also in the amorphous material, and theybehave as if they are crystal grains (clusters). The present inventorshave expressed the intensity of the magnetic coupling force generatedbetween the minute aggregates by using the δM plot described above. Whenno peak is present on the curve of the δM plot for the amorphousmaterial, it is considered that no magnetic coupling force is exertedbetween the minute aggregates. It is considered that the magneticcoupling force between the minute aggregates is small, when the magneticintensity, which is obtained when the peak is obtained, is small. Whenthe magnetic material, which has the magnetic characteristics specifiedby using the δM plot as described above, is used for theinformation-recording film, then it is possible to form the minutemagnetic domains when information is recorded, and it is possible torewrite or erase information with ease. That is, the magnetic recordingmedium, which is suitable to perform the high density recording, can beprovided, for example, by raising the gas pressure when theinformation-recording film is formed, or by dispersing non-magneticcomponent, inorganic compound, oxide, and/or nitride in theinformation-recording film so that the information-recording film of themagnetic recording medium satisfies the conditions described above.

According to a sixth aspect of the present invention, there is provideda magnetic recording apparatus comprising:

-   -   the magnetic recording medium according to any one of the first,        second, and fifth aspects of the present invention;    -   a magnetic head which records or reproduces information; and    -   a drive unit which drives the magnetic recording medium.

The magnetic recording apparatus according to the present invention isinstalled with the magnetic recording medium according to any one of thefirst, second, and fifth aspects of the present invention. Therefore, itis possible to record information including, for example, images,voices, and code data correctly at a super high density. Therefore, itis possible to provide the magnetic recording apparatus having a largestorage capacity.

The magnetic head of the magnetic recording apparatus of the presentinvention can carry a reproducing element which has such acharacteristic (magneto-resistance effect) that the resistance ischanged corresponding to the change of the magnetic flux generated fromthe magnetic recording medium, including, for example, the MR element(Magneto Resistive element, magneto-resistance effect element), the GMRelement (Giant Magneto Resistive element, giant magneto-resistanceeffect element), and the TMR element (Tunneling Magneto Resistiveelement, magneto-tunneling type magneto-resistance effect element). Whensuch a reproducing element is used, the information, which is recordedon the magnetic recording medium, can be reproduced at high S/N.

It is preferable that the magnetic recording apparatus of the presentinvention further comprises an optical head which radiates a light beamfor heating the magnetic recording medium at least when information isrecorded. It is preferable to use light pulses modulated in a form ofpulse as the light beam to be generated from the optical head.Especially, it is most preferable to use a form of multipulse as anaggregate of pulses each having a definite width.

In the magnetic recording apparatus as described above, information canbe recorded by applying a magnetic field from the magnetic head to alight-irradiated area simultaneously with irradiation of the magneticrecording medium with the pulse-shaped light beam when the informationis recorded. In this procedure, the magnetic field, which is applied tothe magnetic recording medium, may be a pulsed magnetic field which issynchronized with the pulsed light beam. As described above, when themagnetic field is applied with the magnetic head having a narrowmagnetic gap to perform recording at a high frequency simultaneouslywith the irradiation of the magnetic recording medium with the pulsedlight beam when information is recorded, it is possible to form minuterecording magnetic domains. For example, the recording frequency of themagnetic head can be not less than 30 MHz, and more preferably not lessthan 50 MHz. Accordingly, information can be recorded at a high density.When the laser beam is radiated from the optical head onto the magneticrecording medium, then the light energy is converted into the thermalenergy in the information-recording film (amorphous magnetic film ormagnetic film) of the magnetic recording medium, and the coercivity ofthe light-irradiated area of the information-recording film is lowered.It is necessary to perform recording at a high velocity by applying themagnetic field at a high recording frequency from the magnetic head tothe information-recording film in which the coercivity is lowered. Asdescribed above, in the magnetic recording apparatus of the presentinvention, the coercivity of the information-recording film can belowered by means of the heating with light during the recording ofinformation. Therefore, information can be reliably recorded even in thecase of the use of the magnetic recording medium provided with theinformation-recording film having the high coercivity. That is,information can be recorded on the magnetic recording medium providedwith the information-recording film having the coercivity higher than 5kOe (about 397.9 kA/m), because the ordinary magnetic head can generatethe magnetic field of about 5 kOe (about 397.9 kA/m). Therefore, themagnetic recording apparatus is preferably used for the high densityrecording.

In the magnetic recording apparatus as described above, information canbe recorded or erased by forming the magnetic domain having a definitewidth and a definite length by using the recording magnetic head. Therecording magnetic domain can be formed so that the width of therecording magnetic domain in the track direction formed in theinformation-recording film is narrower than the gap width of therecording magnetic head. That is, it is possible to form the extremelyminute magnetic domain in the information-recording film by applying themagnetic field while lowering the coercivity of theinformation-recording film by radiating the light beam from the opticalhead. Conventionally, in order to miniaturize the magnetic domain formedin the magnetic recording medium in accordance with the magneticrecording system, it has been necessary that the gap length of themagnetic head is shortened and the track width is narrowed. However, ithas been difficult to obtain such a minute magnetic domain due to theproblem of machining for the magnetic head and the limit concerning theservo operation. On the other hand, in order to allow the minutemagnetic domain to exist stably, it is necessary to raise the coercivityof the magnetic film. However, in the present circumstances, themagnetic head involves a certain limit for the magnetic intensity whichcan be generated, and it has been difficult to magnetize the magneticfilm having high coercivity. Further, in the case of the reproducingsystem based on the use of the magneto-optical effect as in themagneto-optical recording system, the wavelength of light is greatlyrestricted, which is not necessarily suitable for the high densityrecording. Therefore, the method, in which information is recorded,reproduced, and erased by applying the magnetic field while heating themedium by radiating the light beam as in the magnetic recordingapparatus described above, is an effective means to realize the highdensity recording.

Information in a variety of forms can be recorded, reproduced, anderased with the magnetic recording apparatus of the present invention.It is especially preferable that the information to be recorded,reproduced, or erased is at least one type of information selected from,for example, voice information, code data, image information, andcontrol information for controlling the magnetic recording apparatus.

The magnetic recording apparatus of the present invention makes itpossible to realize the high density recording in which the arealrecording density of the magnetic recording medium exceeds 40Gbits/inch² (6.20 Gbits/cm²).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a cross-sectional structure of a magneticrecording medium according to the present invention.

FIG. 2 schematically shows an arrangement on an upper surface of themagnetic recording apparatus as an example of the present invention.

FIG. 3 shows a schematic sectional view illustrating the magneticrecording apparatus taken in the direction of A-A′ shown in FIG. 2.

FIG. 4 schematically shows situations of states of magnetization ofrecorded portions by means of observation with MFM, wherein FIG. 4(A)shows a situation of the state of magnetization of the recorded portionof the magnetic recording medium of the present invention, and FIG. 4(B)shows a situation of the state of magnetization of the recorded portionof a conventional magnetic recording medium provided with a magneticfilm based on the Co—Cr—Pt system as an information-recording film.

FIG. 5 shows a schematic arrangement of a magnetic recording apparatusprovided with an optical head used in a fifth embodiment, wherein FIG.5(A) shows a schematic arrangement on the upper surface of the magneticrecording apparatus, and FIG. 5(B) shows a partial magnified sectionalview illustrating those disposed in the vicinity of a magnetic head ofthe magnetic recording apparatus shown in FIG. 5(A).

FIG. 6 shows another schematic arrangement different from thearrangement of the fifth embodiment, of a magnetic recording apparatusprovided with an optical head, illustrating a situation in which amagnetic head and the optical head are arranged on the same side withrespect to a magnetic disk.

FIG. 7 schematically shows a cross-sectional structure of a magneticrecording medium manufactured in an eighth embodiment.

FIG. 8 schematically shows a cross-sectional structure of a magneticrecording medium manufactured in an embodiment.

FIG. 9 schematically shows situations of states of magnetization ofrecorded portions obtained by observation with MFM, illustrating asituation of the state of magnetization of the recorded portion of amagnetic recording medium according to the present invention and asituation of the state of magnetization of the recorded portion of aconventional magnetic recording medium provided with a magnetic filmbased on the Co—Cr—Pt system as an information-recording film.

FIG. 10 illustrates the magnetic wall movement in magnetic films,wherein FIG. 10(A) shows a case of the present invention in which oxideor nitride is contained in the magnetic film, and FIG. 10(B) shows aconventional case.

FIG. 11 schematically shows a result of Auger analysis for the crosssection of a magnetic film of a magnetic recording medium manufacturedin a third embodiment.

FIG. 12 shows an MFM image obtained by observing a surface of a magneticfilm alternately stacked with layers containing oxygen and layerscontaining no oxygen after AC demagnetization with MFM (magnetic forcemicroscope).

FIG. 13 shows an MFM image obtained by observing a surface of aconventional magnetic film containing no oxygen after AC demagnetizationwith MFM.

FIG. 14 shows a plan view schematically illustrating the positionalrelationship between targets and a substrate of a sputtering apparatusof the substrate rotation type, and a schematic sectional view in whichthe sputtering apparatus is viewed in the direction of X.

FIG. 15 schematically shows a cross-sectional structure of a magneticrecording medium manufactured in an embodiment.

FIG. 16 schematically shows a cross-sectional structure of aninformation-recording film obtained by TEM observation.

FIG. 17 shows results of measurement for the δM plot forinformation-recording films formed with different electric discharge gaspressures in a sixteenth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Specified embodiments of the magnetic recording medium of the presentinvention and the magnetic recording apparatus provided with the samewill be explained in detail below with reference to the drawings.

First Embodiment

In this embodiment, a magnetic recording medium having a cross-sectionalstructure as shown in a schematic sectional view in FIG. 1 wasmanufactured as a magnetic recording medium according to the firstaspect of the present invention. The magnetic recording medium 10 has astructure in which an underlying base film 2, an information-recordingfilm 3, a ferromagnetic film 4, and a protective film 5 are successivelystacked on a substrate 1. In FIG. 1, the information-recording film 3 iscomposed of an artificial lattice film of Tb/Fe/Co, and theferromagnetic film 4 is composed of a Co—Cr alloy film. A method forproducing the magnetic recording medium 10 will be explained below.

Formation of Underlying Base Film

At first, a glass substrate having a diameter of 2.5 inches (about 6.35cm) was prepared as the substrate 1. Subsequently, a silicon nitridefilm was formed as the underlying base film 2 to have a film thicknessof 10 nm on the substrate 1. The underlying base film 2 is a layer whichis provided in order to improve the protection of theinformation-recording film 3 and the adhesive performance with respectto the substrate 1. The magnetron sputtering method was used to form theunderlying base film 2. Si₃N₄ was used for the target, and Ar was usedfor the electric discharge gas. The electric discharge gas pressure was10 mTorr (about 1.33 Pa), and the introduced RF electric power was 1kW/150 mmφ.

Formation of Information-Recording Film

Subsequently, the information-recording film 3 was formed on theunderlying base film 2. The information recording film 3 is anartificial lattice film obtained by periodically stacking thin filmseach having a three layered structure composed of a Tb layer, an Felayer, and a Co layer. The film thickness of each of the layers of thethin film having the three-layered structure is Fe (1 nm)/Co (0.1 nm)/Tb(0.2 nm). The multi-source co-sputtering method based on three sourcesof Tb, Fe, and Co was used as a method for forming theinformation-recording film (artificial lattice film) 3 as describedabove. The film thickness of each of the layers of the thin film havingthe three-layered structure can be precisely controlled to have adesired value by combining the velocity of revolution of the substrateand the electric power introduced during the sputtering. In this case,the introduced DC electric power was 0.3 kW during the formation of theTb film, it was 0.15 kW during the formation of the Co film, and it was0.7 kW during the formation of the Fe film. The number of revolutions ofthe substrate was 30 rpm. High purity Ar gas was used for the electricdischarge gas. The electric discharge gas pressure during the sputteringwas 3 mTorr (about 399 mPa). The artificial lattice film(information-recording film), which had the structure comprising theperiodically stacked three-layered thin films of Fe (1 nm)/Co (0.1nm)/Tb (0.2 nm), was formed to have a film-thickness of about 40 nmunder the sputtering condition as described above. The artificiallattice film is an amorphous magnetic film of the magnetic wall movementtype.

When the artificial lattice film as described above is formed, thedegree of vacuum at the initial evacuation is important. In thisembodiment, the film was formed after effecting the evacuation up to4×10⁻⁹ Torr (about 532×10⁹ Pa). The numerical values, which are adoptedin this embodiment when the information-recording film 3 is formed, arenot absolute, which change depending on, for example, the system of thesputtering. When the information-recording film 3 is constructed as theartificial lattice film as described above, then it is possible toincrease the perpendicular magnetic anisotropy energy as compared with acase in which an amorphous alloy film of Tb—Fe—Co is used as aninformation-recording film, and it is possible to improve the thermalstability of the information-recording film. The magnetization of theinformation-recording film 3 is determined by the difference between themagnetization of the transition metal and the magnetization of the rareearth element. This embodiment was designed so that the magnetization ofthe transition metal was dominant as compared with the magnetization ofthe rare earth element.

Formation of Ferromagnetic Film

Subsequently, a CO₆₇Cr₃₃ film was formed as the ferromagnetic film 4 onthe information-recording film 3. The ferromagnetic film 4 was formed tohave a film thickness of 15 nm so that the magnetic exchange interactionwas generated with respect to the information-recording film 3. The filmthickness is the maximum film thickness at which the exchange couplingforce is exerted with respect to the information-recording film 3. Whenthe ferromagnetic film 4 was formed, the film was continuously formedwithout breaking the vacuum during the process after forming theTb/Fe/Co artificial lattice film as the information-recording film 3 inorder to generate the magnetic coupling.

It is noted that the Co—Cr film, which serves as the ferromagnetic film4, does not exhibit satisfactory magnetization unless crystallization iseffected. For this reason, the sputtering method, which utilized theresonance absorption represented by the ECR (Electron CyclotronResonance) sputtering method, was used. That is, the particles, whichwas excited by the resonance absorption, were allowed to collide withthe target, and the generated sputtering particles were subjected to thesputtering while constantly uniformizing the energy possessed by theparticles by applying a constant drawing voltage as a bias between thetarget and the substrate. As for the conditions for the sputtering, thepressure during the sputtering was 0.3 mTorr (about 39.9 mPa), and theintroduced microwave electric power was 0.7 kW. In order to draw theplasma excited by the microwave, a DC bias voltage of 500 V was applied.Ar was used for the sputtering gas.

When the method as described above is used, the film can be formed at alow temperature without raising the substrate temperature. Therefore, itis possible to suppress the interlayer diffusion which would beotherwise caused with respect to the Tb/Fe/Co artificial lattice film.If such interlayer diffusion takes place, it is especially feared thatthe perpendicular magnetic anisotropy energy may be lowered and thecoercivity may be lowered. Therefore, it is desirable that the substratetemperature is low during the film formation. Therefore, the ECRsputtering method as described above is an effective film formationtechnique as a method for forming the crystalline magnetic film such asthe Co—Cr-based magnetic film at a low temperature. Further, when theTb—Fe—Co amorphous alloy is used, a Co—Cr film can be also formedwithout crystallizing the thin film.

Formation of Protective Film

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 5 on the ferromagnetic film 4 obtained asdescribed above. The ECR sputtering method based on the use of themicrowave was used for the film formation. C (carbon) was used for thetarget material, and Ar was used for the electric discharge gas. Thepressure during the sputtering was 0.3 mTorr (about 39.9 mPa), and theintroduced microwave electric power was 0.5 kW. A DC bias voltage of 500V was applied in order to draw the plasma excited by the microwave. Thequality of the carbon film greatly depends on the sputtering conditionsand the electrode structure as described above. Therefore, the foregoingconditions are not absolute. Thus, the magnetic recording medium havingthe stacked structure shown in FIG. 1 was obtained.

Measurement of Magnetic Characteristics

Subsequently, magnetic characteristics of the manufactured magneticrecording medium 10 were measured. An M-H loop was obtained by themeasurement with VSM (Vibration Sample Magnetometer). According to theobtained results, both of the rectangularity ratios S, S* were 1.0,exhibiting good rectangularity. The coercivity Hc was 3.9 kOe (about310.362 kA/m). The perpendicular magnetic anisotropy energy in thedirection perpendicular to the substrate surface of theinformation-recording film was 4×10⁷ erg/cm³.

Measurement of Volume of Activation

Subsequently, the volume of activation of the magnetic recording medium10 was measured. When the volume of activation is measured, the magneticdomains recorded in the information-recording film were observed withMFM or a polarization microscope to determine the volume of activationby measuring the size of the magnetic domain. As a result of themeasurement of the volume of activation, the volume of activation of theinformation-recording film of the magnetic recording medium of thisembodiment was extremely large, i.e., about five times the value of aCo—Cr—Pt-based magnetic film widely used as the magnetic recordingmedium. This fact indicates that the information-recording film of thisembodiment has small thermal fluctuation and small thermaldemagnetization, and it is excellent in thermal stability.

Measurement of Saturation Magnetization

Subsequently, the saturation magnetization was measured for theinformation-recording film 3 and the ferromagnetic film 4. Thesaturation magnetization of the ferromagnetic film 4 was 380 emu/cm³which was a value larger than that of the saturation magnetization of230 emu/cm³ of the information-recording film 3. It was revealed by themeasurement with a vibration sample magnetometer (VSM) that the exchangecoupling force between the information-recording film 3 and theferromagnetic film 4 was strong, and the information-recording film 3and the ferromagnetic film 4 magnetically behaved as a monolayer film.As described above, the reason why the material having the saturationmagnetization larger than that of the information-recording film 3 isused for the ferromagnetic film 4 is that it is intended to increase,with the ferromagnetic film 4, the magnetic flux coming from themagnetic domain formed in the information-recording film 3. Accordingly,when the magnetic recording medium is subjected to reproduction by usingthe magnetic head, a large reproduction output is obtained.

Subsequently, the structures of the information-recording film 3 and theferromagnetic film 4 were investigated by means of the X-ray diffractionmethod. As a result, only a diffraction peak based on Co—Cr of theferromagnetic film 4 was obtained. The organizations and the structuresof the information-recording film 3 and the ferromagnetic film 4 wereinvestigated by means of a high resolution transmission electronmicroscope (high resolution TEM). As a result, a distinct lattice wasfound for only the Co—Cr film as the ferromagnetic film 4. According tothis result, it was revealed that the other films were amorphous oraggregates of extremely fine organizations. Especially, it was revealedthat the information-recording film 3 was the artificial lattice filmhaving a desired film thickness composed of thin films of thethree-layered structure of Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm). The filmthicknesses of the respective layers of the thin film having thethree-layered structure were well coincident with the measured valuesobtained with the X-ray.

Magnetic Recording Apparatus

Subsequently, a lubricant was applied onto the protective film 5, andthus the magnetic disk was completed. A plurality of magnetic disks weremanufactured in accordance with the same process, and they werecoaxially incorporated into the magnetic recording apparatus. Aschematic arrangement of the magnetic recording apparatus is shown inFIGS. 2 and 3. FIG. 2 shows a top view of the magnetic recordingapparatus 200, and FIG. 3 shows a sectional view taken in the directionalong a broken line A-A′ shown in FIG. 2 of the magnetic recordingapparatus 200. A thin film magnetic head, which was based on the use ofa soft magnetic film having a high saturation magnetic flux density of2.1 T, was used for the recording magnetic head. A recorded signal wasreproduced with a GMR magnetic head of the dual spin bulb type havingthe giant magnetic resistance effect. The gap length of the magnetichead was 0.12 μm. The recording magnetic head and the reproducingmagnetic head are integrated into one unit which is shown as themagnetic head 53 in FIGS. 2 and 3. The integrated type magnetic head iscontrolled by a magnetic head-driving system 54. The plurality ofmagnetic disks 10 are coaxially rotated by a spindle 52. The distancebetween the magnetic head surface and the amorphous magnetic film wasmaintained to be 12 nm. A signal (700 kFCI) corresponding to 40Gbits/inch² (6.20 Gbits/cm²) was recorded on the magnetic disk 10 toevaluate S/N of the disk. As a result, a reproduction output of 34 dBwas obtained. The error rate or defect rate of the magnetic disk wasmeasured. As a result, a value of not more than 1×10⁻⁵ was obtained whenno signal processing was performed.

MFM Observation for Magnetization State

The magnetization state of the recorded portion (recording magneticdomain) was observed with a magnetic force microscope (MFM). As a resultof the observation, the zigzag pattern peculiar to the magnetizationtransition area was not observed. FIG. 4(A) schematically shows asituation of the magnetization state of the recorded portion. It isconsidered that the noise level is extremely small as compared with aconventional magnetic recording medium provided with aninformation-recording film based on the Co—Cr—Pt system, because thezigzag pattern peculiar to the magnetization transition area scarcelyexists in the magnetic recording medium of the embodiment of the presentinvention. Further, it is considered that the low noise level is alsocaused by the fact that the information-recording film is the aggregateof fine and minute grains. For the purpose of comparison, the recordingwas performed in the same manner as described above on the conventionalmagnetic recording medium provided with the information-recording filmbased on the Co—Cr—Pt system to observe the magnetization state of therecorded portion of the information-recording film. FIG. 4(B)schematically shows a situation of the magnetization state. As shown inFIG. 4(B), minute inverse magnetic domains, which had the magnetizationin the direction opposite to the surroundings, were observed in therecording magnetic domains and between the mutually adjoining recordingmagnetic domains. On the other hand, in the case of the magneticrecording medium of this embodiment, as shown in FIG. 4(A), the minuteinverse magnetic domain was scarcely observed in the recording magneticdomains and between the mutually adjoining recording magnetic domains.One of the causes of the low noise level is also the fact that theminute inverse magnetic domain scarcely exists in the recording magneticdomains and between the mutually adjoining recording magnetic domains.

This embodiment is illustrative of the case in which the Tb/Fe/Co systemis used for the artificial lattice film for constructing theinformation-recording film. However, any one of the rare earth elementsof Gd, Dy, and Ho may be used in place of Tb. The information-recordingfilm may be constructed with two rare earth elements such as Gd—Tb,Gd—Dy, Gd—Ho, Tb—Dy, and Tb—Ho. The two-layered film of Fe/Co comprisingthe thin film composed of Fe and the thin film composed of Co was usedas the iron family metal film for constructing the artificial latticefilm. However, the artificial lattice film may be also constructed witha monolayer film composed of an alloy such as Fe—Co, Fe—Ni, and Co—Ni.

The underlying base film 2 is not necessarily formed in the stackedstructure shown in FIG. 1. It is also possible to form a magnetic wallmovement control film for controlling the movement of the magnetic wallof the recording magnetic domain formed in the information-recordingfilm, in place of the underlying base film 2 as described above.

The underlying base film 2 may be formed as a film in accordance withthe reactive sputtering method by using Si as the target and Ar/N₂ asthe electric discharge gas. A film of oxide such as silicon oxide,nitride (for example, aluminum nitride) other than silicon nitride, andoxynitride such as Si—Al—O—N may be used for the underlying base filmother than silicon nitride.

The information-recording film has been formed by means of the DCmagnetron sputtering method. However, in the present invention, thesputtering method (ECR sputtering method) based on the use of theelectron cyclotron resonance and the RF magnetron sputtering method maybe used.

In this embodiment, the Co—Cr system was used for the ferromagneticfilm. However, a ferromagnetic film based on, for example, the Co—Cr—Tasystem, the Co—Cr—Pt system, or the Co—Cr—Pt—Ta system may be used. Inthis case, the ratio between the concentration of Co and theconcentration of the element other than Co is important, and the ratiodetermines the perpendicular magnetic anisotropy energy. Theconcentration of Co in the ferromagnetic film is preferably about 60 at% to 70 at %. The reason why the Co-based material is used for theferromagnetic film in this embodiment is that such a material has thelarge saturation magnetization as compared with an Fe-based material.

For example, a ferromagnetic material based on the CoO or Co—CoO system,which has the perpendicular magnetic anisotropy and which has thesaturation magnetization larger than that of the information-recordingfilm, can be also used for the ferromagnetic film.

When the protective film was formed, Ar was used for the sputtering gas.However, the film may be formed by using a gas containing nitrogen. Whenthe gas containing nitrogen is used, then the grains are made fine andminute, an obtained protective film (carbon film) is densified, and itis possible to further improve the protection performance. The reasonwhey the ECR sputtering method is used to manufacture the protectivefilm is that the carbon film, which is dense and free from pin hole andwhich has good coverage, is obtained even in the case of an extremelythin film of 2 to 3 nm. Additionally, this method also has such afeature that it is possible to extremely decrease the damage received bythe information-recording film when the protective film is manufactured.The deterioration of magnetic characteristics caused by the damagereceived during the film formation is lethal, because theinformation-recording film is progressively made thin as the realizationof high density is advanced. The DC sputtering method may be also usedto form the protective film besides the ECR sputtering method. In thiscase, it is desirable that the DC sputtering method is used when thefilm thickness of the protective film to be formed is not less than 5nm. The DC sputtering method is sometimes disadvantageous when the filmthickness is thinner than the above, for example, for the followingreason. That is, (1) it is feared that the coverage of the surface ofthe information-recording film may be deteriorated, and (2) it is fearedthat the density and the hardness of the protective film may beinsufficient.

Second Embodiment

In this embodiment, a magnetic recording medium having thecross-sectional structure as shown in the schematic sectional view inFIG. 1 was manufactured in the same manner as in the first embodiment.With reference to FIG. 1, an information-recording film 3 is composed ofan amorphous alloy film of Tb—Fe—Co, and a ferromagnetic film 4 iscomposed of an alloy film of Co—Cr. A method for producing the magneticrecording medium 10 will be explained below.

Formation of Underlying Base Film

At first, a glass substrate having a diameter of 2.5 inches (about 6.35cm) was prepared as the substrate 1. Subsequently, a silicon nitridefilm was formed as the underlying base film 2 to have a film thicknessof 10 nm on the substrate 1. The underlying base film 2 is a layer whichis provided in order to improve the protection of theinformation-recording film 3 and the adhesive performance with respectto the substrate 1. The magnetron sputtering method was used to form theunderlying base film 2. Si₃N₄ was used for the target, and Ar was usedfor the electric discharge gas. The electric discharge gas pressure was10 mTorr (about 1.33 Pa), and the introduced RF electric power was 1kW/150 mmφ.

Formation of Information-Recording Film

Subsequently, a film of Tb₁₉Fe₇₁Co₁₀ was formed as theinformation-recording film 3 on the underlying base film 2 by using themagnetron sputtering method to have a film thickness of 20 nm. ATb—Fe—Co alloy, which had a composition with dominant sub-latticemagnetization of the transition metal, was used for the sputteringtarget, and pure Ar was used for the electric discharge gas. Theelectric discharge gas pressure during the sputtering was 5 mTorr (about665 mPa), and the introduced RF electric power was 1 kW/150 mmφ.

Formation of Ferromagnetic Film

Subsequently, a CO₆₇Cr₃₃ film was formed as the ferromagnetic film 4 onthe information-recording film 3. The ferromagnetic film 4 was formed tohave a film thickness of 8 nm so that the magnetic exchange interactionwas generated with respect to the information-recording film 3. The filmthickness is the maximum film thickness at which the exchange couplingforce is exerted with respect to the information-recording film 3. Whenthe ferromagnetic film 4 was formed, the film was continuously formedwithout breaking the vacuum during the process after forming theTb—Fe—Co film as the information-recording film 3 in order to generatethe magnetic coupling.

When the Co—Cr film as the ferromagnetic film 4 was formed, the ECRsputtering method was used in the same manner as in the firstembodiment. As for the conditions for the sputtering, the pressureduring the sputtering was 3 mTorr (about 399 mPa), and the introducedmicrowave electric power was 1 kW. In order to draw the plasma excitedby the microwave, a DC bias voltage of 500 V was applied. Ar was usedfor the sputtering gas.

The value of the saturation magnetization of the Co—Cr film as theferromagnetic film was 380 emu/cm³, and the saturation magnetization ofthe Tb—Fe—Co film as the information-recording film was 230 emu/cm³. Thesaturation magnetization of the ferromagnetic film was larger than thesaturation magnetization of the information-recording film. It wasrevealed by the measurement with a vibration sample magnetometer (VSM)that the exchange coupling force between the Co—Cr film and the Tb—Fe—Cofilm was strong, and the Co—Cr film and the Tb—Fe—Co film magneticallybehaved as a monolayer film.

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 5 on the ferromagnetic film 4. The ECR sputteringmethod based on the use of the microwave was used for the filmformation. C (carbon) was used for the target material, and Ar was usedfor the electric discharge gas. The pressure during the sputtering was 3mTorr (about 399 mPa), and the introduced microwave electric power was 1kW. A DC bias voltage of 500 V was applied in order to draw the plasmaexcited by the microwave. The quality of the carbon film greatly dependson the sputtering conditions as described above and the electrodestructure. Therefore, the foregoing conditions are not absolute. Thus,the magnetic recording medium having the stacked structure shown in FIG.1 was obtained.

Measurement of Magnetic Characteristics

Subsequently, magnetic characteristics of the manufactured magneticrecording medium were measured. An M-H loop was obtained by themeasurement with VSM (Vibration Sample Magnetometer). According to theobtained results, both of the rectangularity ratios S, S* were 1.0,exhibiting good rectangularity. The coercivity Hc was 3.5 kOe (about278.53 kA/m). The perpendicular magnetic anisotropy energy in thedirection perpendicular to the substrate surface of theinformation-recording film was 2×10′ erg/cm³. The in-plane magneticanisotropy energy in the direction parallel to the substrate surface was1×10⁴ erg/cm³.

Measurement of Volume of Activation

Subsequently, the volume of activation of the magnetic recording mediumwas measured. When the volume of activation is measured, the magneticdomains recorded in the information-recording film were observed withMFM or a polarization microscope to determine the volume of activationby measuring the size of the magnetic domain. As a result of themeasurement of the volume of activation, the volume of activation of theinformation-recording film of the magnetic recording medium of thisembodiment was extremely large, i.e., about forty times the value of aCo—Cr—Pt-based magnetic film widely used as the magnetic recordingmedium. This fact indicates that the information-recording film of thisembodiment has small thermal fluctuation and small thermaldemagnetization, and it is excellent in thermal stability.

Subsequently, the structures of the information-recording film 3 and theferromagnetic film 4 were investigated by means of the X-ray diffractionmethod. As a result, only a diffraction peak based on Co—Cr of theferromagnetic film 4 was obtained. The organizations and the structuresof the information-recording film 3 and the ferromagnetic film 4 wereinvestigated by means of a high resolution transmission electronmicroscope (high resolution TEM). As a result, a distinct lattice wasfound for only the Co—Cr film as the ferromagnetic film 4. According tothis result, it was revealed that the other films were amorphous oraggregates of extremely fine organizations.

Magnetic Recording Apparatus

Subsequently, a lubricant was applied onto the protective layer in thesame manner as in the first embodiment to manufacture a plurality ofmagnetic disks. The plurality of obtained magnetic disks were coaxiallyincorporated into the magnetic-recording apparatus. The arrangement ofthe magnetic recording apparatus was the same as that used in the firstembodiment, which was constructed as shown in FIGS. 2 and 3.

The magnetic recording apparatus was driven to evaluate recording andreproduction characteristics of the magnetic disk. When the recordingand reproduction characteristics were evaluated, the distance betweenthe magnetic head and the magnetic recording medium was maintained to be12 nm. A signal (700 kFCI) corresponding to 40 Gbits/inch² (6.20Gbits/cm²) was recorded on the disk to evaluate SIN of the disk. As aresult, a reproduction output of 34 dB was obtained. The error rate ordefect rate of the disk was measured. As a result, a value of not morethan 1×10⁻⁵ was obtained when no signal processing was performed.

MFM Observation for Magnetization State

The magnetization state of the recorded portion (recording magneticdomain) was observed with a magnetic force microscope (MFM). As a resultof the observation, the zigzag pattern peculiar to the magnetizationtransition area was not observed. It is considered that the noise levelis extremely small as compared with a conventional magnetic recordingmedium provided with an information-recording film based on the Co—Cr—Ptsystem, because the zigzag pattern peculiar to the magnetizationtransition area scarcely exists in the magnetic recording medium of theembodiment of the present invention. Further, it is considered that thelow noise level is also caused by the fact that theinformation-recording film is amorphous. For the purpose of comparison,the recording was performed in the same manner as described above on theconventional magnetic recording medium provided with theinformation-recording film based on the Co—Cr—Pt system to observe themagnetization state of the recorded portion of the information-recordingfilm. As a result of the observation, minute inverse magnetic domains,which had the magnetization in the direction opposite to thesurroundings, were observed in the recording magnetic domains andbetween the mutually adjoining recording magnetic domains. On the otherhand, in the case of the magnetic recording medium of this embodiment,the minute inverse magnetic domain was scarcely observed in therecording magnetic domains and between the mutually adjoining recordingmagnetic domains. One of the causes of the low noise level is also thefact that the minute inverse magnetic domain scarcely exists in therecording magnetic domains and between the mutually adjoining recordingmagnetic domains.

This embodiment is illustrative of the case in which the magneticmaterial based on the Tb—Fe—Co system is used for theinformation-recording film. However, any one of the rare earth elementsof Gd, Dy, and Ho may be used in place of Tb. The information-recordingfilm may be constructed with two rare earth elements such as Gd—Tb,Gd—Dy, Gd—Ho, Tb—Dy, and Tb—Ho. The Fe—Co alloy was used for the ironfamily metal film. However, the information-recording film may be alsoconstructed with an alloy such as Fe—Co, Fe—Ni, and Co—Ni.

The underlying base film 2 may be formed as a film in accordance withthe reactive sputtering method by using Si as the target and Ar/N₂ asthe electric discharge gas. A film of oxide such as silicon oxide,nitride (for example, aluminum nitride) other than silicon nitride, andoxynitride such as Si—Al—O—N may be used for the underlying base filmother than silicon nitride.

The magnetic material based on the Co—Cr system is used for theferromagnetic film 4. However, a magnetic material based on the Co—Cr—Tasystem or the Co—Cr—Pt system may be used.

Third Embodiment

In this embodiment, a magnetic recording medium having the same stackedstructure as that shown in FIG. 1 was manufactured by using the samematerials and the same method as those used in the first embodimentexcept that a substrate having a concave/convex texture on a substratesurface was used. The formation of the texture on the substrate surfaceincludes, for example, (1) a method in which the substrate surface isprepared simultaneously with the polishing and (2) a method in which anextremely thin film in an island form is formed to use it as a texture.Any one of the methods may be used. The respective layers 2 to 5 shownin FIG. 1 were stacked in the same manner as in the first embodiment onthe substrate having the texture as described above to manufacture themagnetic recording medium.

Magnetic characteristics were investigated for the obtained magneticrecording medium. As a result, it was revealed that the obtainedmagnetic recording medium had magnetic characteristics equivalent tothose of the magnetic recording medium manufactured in the firstembodiment. Subsequently, a plurality of magnetic disks weremanufactured in the same manner as in the first embodiment, and theplurality of obtained magnetic disks were coaxially incorporated intothe magnetic recording apparatus. The magnetic recording apparatus wasconstructed in the same manner as in the first embodiment, which had thestructure as shown in FIGS. 2 and 3.

The magnetic recording apparatus was driven to evaluate recording andreproduction characteristics of the magnetic disk. As a result, thenoise level was lower by about 1 dB than that of the magnetic disk inthe first embodiment. It has been revealed from the analysis by MFM thatthe reason why the noise level is lowered as described above is that themovement of the magnetic wall of the recording magnetic domain issuppressed by the convex/concave unevenness of the texture formed on thesubstrate surface, and the zigzag pattern in the area of inversion ofmagnetization is flat after recording information.

The effect to suppress the magnetic wall movement brought about by thetexture on the substrate does not depend on the magnetic material to beused. Convex/concave unevenness may be formed on the surface of theunderlying base film before forming the information-recording film, inplace of the provision of the texture on the substrate surface.According to this embodiment, it is appreciated that the substratehaving the texture on the surface is effective to improve the accuracyof formation of the recording magnetic domain and reduce the noise.

Fourth Embodiment

In this embodiment, a magnetic recording medium was produced by usingthe same materials and the same method as those used in the firstembodiment except that a Co/Pt alternately stacked multilayered film wasused for the ferromagnetic film. The structure of the magnetic recordingmedium is the same as that of the magnetic recording medium in the firstembodiment. Reference may be made to FIG. 1. Explanation will be madebelow for only a method for forming the Co/Pt alternately stackedmultilayered film as the ferromagnetic film. The method for forming thelayers other than the ferromagnetic film is the same as that used in thefirst embodiment, explanation of which will be omitted.

Formation of Ferromagnetic Film

A Pt/Co alternately stacked multilayered film was formed as aferromagnetic film 4 to have a film thickness of 8 nm on theinformation-recording film 3. The Pt/Co alternately stacked multilayeredfilm is obtained by successively and periodically stacking thin filmseach having a two-layered structure composed of a Pt thin film and a Cothin film. The multi-source co-sputtering method based on two sources ofPt and Co was used to form the Pt/Co alternately stacked multilayeredfilm. In this embodiment, the film thickness of each of the layers ofthe thin film having the two-layered structure was Pt (0.5 nm)/Co (0.9nm). The film thickness of each of the layers of the thin film havingthe two-layered structure can be precisely controlled to have a desiredvalue by combining the velocity of revolution of the substrate and theintroduced electric power during the sputtering. In this embodiment, theintroduced DC electric power was controlled to be 0.3 kW during theformation of the Pt film, and it was controlled to be 0.6 kW during theformation of the Co film. The number of revolutions of the substrateduring the film formation was 30 rpm. The electric discharge gaspressure during the sputtering was 3 mTorr (about 399 mPa), and a highpurity Ar gas was used for the electric discharge gas.

When the alternately stacked multilayered film as described above ismanufactured, the degree of vacuum upon the initial evacuation isimportant. In this embodiment, the film formation was started afterperforming the evacuation up to 4×10⁻⁹ Torr. The values are notabsolute, which may be changed depending on, for example, the sputteringsystem. In this embodiment, when the alternately stacked multilayeredfilm was formed, the DC magnetron sputtering method was used. However,it is also allowable to use the RF magnetron sputtering method and thesputtering method (ECR sputtering method) based on the use of theelectron cyclotron resonance. Especially, when the Co layer asaggregates of fine crystals is formed, it is effective to use the ECRsputtering.

Measurement of Magnetic Characteristics

Subsequently, magnetic characteristics of the manufactured magneticrecording medium were measured. According to an M-H loop obtained by themeasurement with VSM, both of the rectangularity ratios S, S* were 1.0,and thus good rectangularity was obtained. The coercivity Hc was 3.9 kOe(about 310.362 kA/m). As for the magnetic anisotropy of theinformation-recording film, the in-plane magnetic anisotropy energy inthe direction parallel to the substrate surface was 1×10′ erg/cm³, andthe perpendicular magnetic anisotropy energy in the directionperpendicular to the substrate surface was 4×10⁷ erg/cm³ Further, thevolume of activation of the magnetic recording medium was measured. As aresult, the volume of activation had an extremely large value, i.e.,about five times that of a magnetic recording medium provided with amagnetic film based on the Co—Cr—Pt system. This fact indicates that thematerial for constructing the information-recording film has smallthermal fluctuation and small thermal demagnetization, and it isexcellent in thermal stability.

Further, the structures of the information-recording film and theferromagnetic film were investigated by means of the X-ray diffractionmethod. As a result, no diffraction peak was obtained. According to thisfact, it is appreciated that the information-recording film and theferromagnetic film are amorphous or aggregates of microcrystals as awhole. The organizations and the structures of the information-recordingfilm and the ferromagnetic film were investigated by means of a highresolution transmission electron microscope (high resolution TEM). As aresult, it was revealed that a lattice was found for only Fe and Cograins contained in the information-recording film and the ferromagneticfilm, and the other portions had an amorphous structure. Especially, itwas revealed that the information-recording film was an artificiallattice film having a desired film thickness in which thin films eachhaving a three-layered structure of Fe (1 nm)/Co (0.1 nm)/Tb (0.1 nm)were periodically stacked. The film thicknesses of the respective layersof the thin film having the three-layered structure were well coincidentwith the measured values obtained by using the X-ray. The ferromagneticfilm was also an alternately stacked multilayered film of Pt/Co.

Subsequently, the volume of activation of the magnetic recording mediumwas measured in accordance with the same method as that used in thefirst embodiment. As a result, the volume of activation was large, i.e.,about five times the value of a Co—Cr—Pt-based magnetic film widely usedfor the magnetic recording medium. This fact indicates the fact that theinformation-recording film is excellent in thermal stability.

Subsequently, a lubricant was applied onto the protective layer in thesame manner as in the first embodiment to manufacture a plurality ofmagnetic disks. The plurality of obtained magnetic disks were coaxiallyincorporated into the magnetic recording apparatus. The arrangement ofthe magnetic recording apparatus was the same as that used in the firstembodiment, which was constructed as shown in FIGS. 2 and 3.

The magnetic recording apparatus was driven to evaluate recording andreproduction characteristics of the magnetic disk. When the recordingand reproduction characteristics were evaluated, the distance betweenthe magnetic head and the magnetic recording medium was maintained to be12 nm. A signal (700 kFCI) corresponding to 40 Gbits/inch² (6.20Gbits/cm²) was recorded on the disk to evaluate S/N of the disk. As aresult, a reproduction output of 34 dB was obtained. The error rate ordefect rate of the disk was measured. As a result, a value of not morethan 1×10⁻⁵ was obtained when no signal processing was performed.

The magnetization state of the recorded portion (recording magneticdomain) was observed with a magnetic force microscope (MFM). As aresult, the zigzag pattern peculiar to the magnetization transition areawas not observed. It is considered that the noise level is extremelydecreased as compared with a magnetic recording medium provided with amagnetic film based on the Co—Cr—Pt system, because the zigzag patternpeculiar to the magnetization transition area scarcely exists in themagnetic recording medium of the embodiment of the present invention.Further, it is considered that the low noise level is also caused by thefact that the magnetic film is an aggregate of fine grains. In themagnetic recording medium of this embodiment, the minute inversemagnetic domains, which had the magnetization in the direction oppositeto the surroundings, were not observed in the recording magnetic domainsand between the mutually adjoining recording magnetic domains. This factis also one of the causes of the low noise level.

In this embodiment, the alternately stacked multilayered film based onthe Co/Pt system was used for the ferromagnetic film. However, Fe or Nimay be used in place of Co. Further, Pd or Rh can be also used in placeof Pt, in which the same or equivalent effect is obtained.

Fifth Embodiment

In this embodiment, a magnetic recording medium having the same stackedstructure as that prepared in the first embodiment (see FIG. 1) wasmanufactured in accordance with the same method as that used in thefirst embodiment except that the film thicknesses of the respectivelayers of the Tb layer, the Fe layer, and the Co layer for constructingthe Tb/Fe/Co artificial lattice film as the information-recording filmwere adjusted in order to enhance the coercivity of theinformation-recording film. The recording can be performed at a higherdensity by increasing the coercivity of the information-recording filmfor recording information therein.

Magnetic characteristics of the obtained magnetic recording medium weremeasured. According to an M-H loop obtained by the measurement with VSM,both of the rectangularity ratios S, S* were 1.0, exhibiting goodrectangularity. The coercivity Hc was 3.9 kOe (about 310.362 kA/m). TheCurie temperature of the information-recording film was 260° C., and thecompensation temperature was not more than the room temperature. Thesub-lattice magnetization of the iron family element was dominant in thecomposition. As a result of the measurement of the magnetic anisotropyof the information-recording film as described above, the in-planemagnetic anisotropy energy in the direction parallel to the substratesurface was 1×10⁴ erg/cm³, and the perpendicular magnetic anisotropyenergy in the direction perpendicular to the substrate was 4×10⁷erg/cm³. The value of the perpendicular magnetic anisotropy energy wasnot less than four times the value of an amorphous alloy of Tb—Fe—Co.

Subsequently, the volume of activation of the magnetic recording mediumwas measured. The volume of activation was measured in the same manneras in the first embodiment. As a result of the measurement of the volumeof activation, the volume of activation of the information-recordingfilm of the magnetic recording medium of this embodiment was extremelylarge, i.e., about six times the value of a magnetic film based on theCo—Cr—Pt system widely used for the magnetic recording medium. Further,the volume of activation of the information-recording film of themagnetic recording medium of this embodiment was 1.2 time the value ofan amorphous alloy based on the Tb—Fe—Co system. This fact indicatesthat the information-recording film of this embodiment is a filmexcellent in thermal stability in which the thermal fluctuation and thethermal demagnetization are small.

Subsequently, the structures of the information-recording film and theferromagnetic film were investigated by means of the X-ray diffractionmethod. As a result, only a diffraction peak based on Co—Cr wasobtained. Further, the organizations and the structures of theinformation-recording film and the ferromagnetic film were investigatedby means of a high resolution transmission electron microscope (highresolution TEM). As a result, it was revealed that a definite latticewas found for only the Co—Cr film as the ferromagnetic film, and theother films were amorphous or aggregates of extremely fineorganizations. Especially, it was found that the information-recordingfilm was an artificial lattice film having a desired film thickness. Thefilm thicknesses of the respective layers of the artificial lattice filmwere well coincident with the measured values obtained by using theX-ray.

Subsequently, the surface of the magnetic recording medium was subjectedto tape cleaning, and then a lubricant was applied to complete themagnetic disk. A plurality of magnetic disks were manufactured inaccordance with the same process. In this embodiment, the obtainedmagnetic disks were coaxially incorporated into the magnetic recordingapparatus as shown in FIG. 5. FIG. 5(A) shows a top view illustratingthe magnetic recording apparatus 300, and FIG. 5(B) shows a partialmagnified sectional view illustrating those disposed in the vicinity ofa magnetic head 53 of the magnetic recording apparatus 300 shown in FIG.5(A).

In the magnetic recording apparatus 300, an optical head 55 and themagnetic head 53 are arranged so that they are opposed to one anotherwith the magnetic disks 51 intervening therebetween as shown in FIG.5(B). The optical head 55 comprises a semiconductor laser (not shown)having a wavelength of 630 nm, and a lens 56 having a numerical apertureNA of 0.60. In FIGS. 5(A) and 5(B), the magnetic head 53 is anintegrated type magnetic head in which a recording magnetic head and areproducing magnetic head are integrated into one unit. A thin filmmagnetic head, which is based on the use of a soft magnetic film havinga high saturation magnetic flux density of 2.1 T, was used for therecording magnetic head. The gap length of the recording magnetic headwas 0.12 μm. A GMR magnetic head of the dual spin bulb type having thegiant magnetic resistance effect was used for the reproducing magnetichead. The integrated type magnetic head 53 is controlled by a magnetichead-driving system 54. The position of the optical head 55 iscontrolled on the basis of control information used for the magnetichead-driving system 54. The plurality of magnetic disks 51 are coaxiallyrotated by a spindle 52. The magnetic head 53 is controlled so that thedistance between the bottom surface of the magnetic head 53 and thesurface of the magnetic disk 51 is 12 nm during recording or duringreproduction of information.

A signal (700 kFCI) corresponding to 40 Gbits/inch² (6.20 Gbits/cm²) wasrecorded on the magnetic disk 51 by driving the magnetic recordingapparatus 300 as described above, and recorded information wasreproduced. As a result, a reproduction output of 36 dB was obtained.The error rate or defect rate of the magnetic disk was measured. As aresult, a value of not more than 6×10⁻⁶ was obtained when no signalprocessing was performed. When information was recorded in thisembodiment, then the optical head 55 was used to continuously radiate amultipulse laser beam having a laser power of 6 mW and a pulse intervalof 20 ns onto the magnetic disk 51, and the magnetic head 53 was used toapply a constantly modulated magnetic field. Information can be alsorecorded on the magnetic disk by radiating minute light pulses having alaser power of 15 mw and a pulse interval of 10 ns from the opticalhead, and applying a pulse magnetic field synchronized with the minutelight pulses by using the magnetic head. Further, information can bealso recorded by applying a magnetic field by using the magnetic headwhile radiating, onto the magnetic disk, a laser beam from the opticalhead in a defocused state.

When the laser beam is radiated onto the magnetic disk during therecording of information as in the magnetic recording apparatus of thisembodiment, then the light absorption occurs in the light-irradiatedarea of the information-recording film, and the light energy isconverted into the thermal energy. Accordingly, the temperature israised and the coercivity is lowered at the light-irradiated portion ofthe information-recording film. Information is recorded bysimultaneously applying, to the light-irradiated portion of theinformation-recording film, the magnetic field having the polaritycorresponding to recording information from the thin film magnetic head.In the magnetic recording apparatus of this embodiment, information canbe recorded reliably at a high density even when the coercivity of theinformation-recording film for constructing the magnetic recordingmedium is higher than the intensity of the applied magnetic fieldapplied by the magnetic head.

The magnetization state of the recorded portion (recording magneticdomain) was observed with a magnetic force microscope (MFM). As a resultof the observation, the zigzag pattern peculiar to the magnetizationtransition area was not observed. As for the size of the formedrecording magnetic domain, the width in the track direction was 70 nm,which was shorter than the gap length of the magnetic head. Wheninformation was recorded by using the pulse magnetic field and the pulselight beam, the width in the track direction of the formed recordingmagnetic domain was 50 nm, which was further shorter than the gap lengthof the magnetic head.

Sixth Embodiment

In this embodiment, the same magnetic recording medium as that used inthe fifth embodiment was used. The magnetic recording medium wasincorporated into the magnetic recording apparatus having the samestructure as that of the magnetic recording apparatus used in the fifthembodiment (see FIG. 5(A)) except that a magnetic head 53′ and anoptical head 55′ were arranged on an identical side with respect to themagnetic disk 51 as shown in FIG. 6. The magnetic recording apparatuswas driven to perform recording/reproduction/erasing.

In the magnetic recording apparatus of this embodiment, the light beam,which is radiated from the optical head 55′, comes into the magneticdisk 51 from the side opposite to the substrate, not from the side ofthe substrate of the magnetic disk 51. In the case of the magneticrecording apparatus as described above, the optical head and themagnetic head can be merged. Therefore, the servo mechanism for the headcan be simplified, and thus the arrangement of the apparatus can besimplified.

The magnetic recording apparatus as described above was driven to recorda signal (700 kFCI) corresponding to 40 Gbits/inch² (6.20 Gbits/cm²) onthe magnetic disk. When information was recorded, the distance betweenthe bottom surface of the magnetic head and the surface of the magneticdisk was maintained to be 12 nm. Information was recorded bycontinuously radiating a multi-pulse laser beam at an interval of 20 nswith a laser power of 6 mW from the optical head onto the magneticrecording medium, and simultaneously applying a constant modulatedmagnetic field from the magnetic head. Information was recorded on themagnetic disk by using the method as described above, and the recordedinformation was reproduced. As a result, a reproduction output of 36 dBwas obtained. Information can be also recorded on the magnetic disk byusing minute light pulses having a laser power of 15 mW and a pulseinterval of 10 ns as the light beam radiated from the optical head, andsynchronizing a pulse magnetic field generated from the magnetic headwith the minute light pulses.

The recording magnetic domain recorded on the magnetic disk was observedwith MFM in the same manner as in the first embodiment. As a result, themagnetic domain, which was smaller than the gap width of the magnetichead, was formed. In the case of the magnetic recording apparatus ofthis embodiment, even when the magnetic film of the magnetic recordingmedium has a coercivity higher than the intensity of the appliedmagnetic field applied by the magnetic head, the recording can beperformed by lowering the coercivity of the magnetic film by means ofthe heating effected by the radiation of the laser beam. Finally, theerror rate or defect rate of the disk was measured. As a result, a valueof not more than 1×10⁻⁵ was obtained when no signal processing wasperformed.

Seventh Embodiment

In this embodiment, a magnetic recording medium having a cross-sectionalstructure as shown in FIG. 7 was manufactured. The magnetic recordingmedium 70 has a structure in which an underlying base film 72, a firstmagnetic film 73, a second magnetic film 74, a third magnetic film 75,and a protective film 76 are successively stacked on a substrate 71. Thefirst magnetic film 73 is a layer (magnetic wall movement control layer)for suppressing the movement of the magnetic wall formed in the secondmagnetic film, and it is constructed with a Co—Cr—Pt film. The secondmagnetic film 74 is a layer (information-recording film) for recordinginformation therein, and it is constructed with a Tb—Fe—Co film. Thethird magnetic film is a layer (reproducing layer) for enhancing thereproduced signal output during reproduction, and it is constructed witha Pt/Co alternately stacked multilayered film. A method for producingthe magnetic recording medium 70 will be explained below.

Formation of Underlying Base Film

At first, a glass substrate having a diameter of 2.5 inches (about 6.35cm³) was prepared as the substrate 71. A Cr₈₀Ti₂₀ alloy film was formedas the underlying base film 72 on the substrate 71 by means of the DCmagnetron sputtering method. The underlying base film 72 is capable ofcontrolling the orientation of the first magnetic film 73. A Cr—Ti alloywas used for the target material, and pure Ar was used for the electricdischarge gas. The pressure during the sputtering was 3 mTorr (about 399mPa), and the introduced DC electric power was 1 kW/150 mmφ. Thesputtering was performed at the room temperature, for the followingreason. That is, when the sputtering is performed at the roomtemperature, then the formed alloy film is fine and minute, andconsequently the crystal grains of the first magnetic film 73 formed onthe underlying base film 72 can be made fine and minute. The filmthickness of the underlying base film 72 was 10 nm.

Formation of First Magnetic Film

Subsequently, a perpendicularly magnetizable film composed ofCO₅₃Cr₃₅Pt₁, was formed as the first magnetic film 73 on the underlyingbase film 72 by means of the DC sputtering method. A Co—Cr—Pt alloy wasused for the target material, and pure Ar was used for the electricdischarge gas. The pressure during the sputtering was 3 mTorr (about 399mPa), and the introduced DC electric power was 1 kW/150 mmφ. Thesubstrate temperature during the film formation was 200° C.

The cross-sectional structure of the formed first magnetic film 73 wasobserved with a transmission electron microscope (TEM). As a result, itwas revealed that the film thickness of the first magnetic film 73 was10 nm, and the first magnetic film 73 was epitaxially grown from theCr—Ti film (underlying base film).

Subsequently, magnetic characteristics of the single first magnetic filmwere investigated. As a result, the coercivity was 2.8 kOe (about222.824 kA/m), the perpendicular magnetic anisotropy energy was 8×10⁵erg/cm³, and the saturation magnetization was 300 emu/ml.

Concave/convex unevenness corresponding to crystal grains in themagnetic film was formed on the surface of the formed first magneticfilm 73. The size of the concave/convex unevenness was investigated. Asa result, the distance in the direction parallel to the substratesurface, which ranged from an apex (center of the convex) of a certainpeak (convex) to an apex (center of the convex) of a peak nearestthereto, was 2 μm. The distance between a peak (center of the convex)and a valley (center of the concave) was 4 nm.

Formation of Second Magnetic Film

Subsequently, an amorphous film of Tb—Fe—Co was formed as the secondmagnetic film 74 on the first magnetic film 73 without breaking thevacuum after the formation of the first magnetic film 73. Thecomposition of the second magnetic film 74 is Tb₂₁Fe₆₉CO₁₀, which is acomposition in which the sub-lattice magnetization of the transitionmetal is dominant. The second magnetic film 74 was formed by using theRF magnetron sputtering method. In the sputtering, a Tb—Fe—Co alloy wasused for the target material, and pure Ar was used for the electricdischarge gas. The formed second magnetic film 74 has a film thicknessof 20 nm. The pressure during the sputtering is 3 mTorr (about 399 mPa),and the introduced DC electric power is 1 kW/150 mmφ.

The coercivity of the obtained second magnetic film 74 was 3.5 kOe(about 278.53 kA/m), the saturation magnetization was 250 emu/ml, andthe perpendicular magnetic anisotropy energy was not less than 7×10⁶erg/cm³.

Formation of Third Magnetic Film

Subsequently, an alternately stacked multilayered film of Pt/Co wasformed as the third magnetic film 75 on the second magnetic film 74. Thethird magnetic film 75 is a layer which is provided in order to improvethe reproduction characteristics. The Pt/Co alternately stackedmultilayered film is obtained by successively and periodically stackingthin films each having a two-layered structure composed of a Pt thinfilm and a Co thin film. When the Pt/Co alternately stacked multilayeredfilm was formed, the two-source co-sputtering method based on two sourcetargets of Pt and Co was used. In this embodiment, the film thickness ofeach of the layers of the thin film having the two-layered structure wasPt (0.5 nm)/Co (0.9 nm). The film thickness of each of the layers of thethin film having the two-layered structure can be precisely controlledto have a desired value by combining the velocity of revolution of thesubstrate and the introduced electric power during the sputtering. Inthis embodiment, the introduced DC electric power was controlled to be0.3 kW during the formation of the Pt film, and the introduced DCelectric power was controlled to be 0.6 kW during the formation of theCo film. The number of revolutions of the substrate during the filmformation is 30 rpm. The electric discharge gas pressure during thesputtering was 3 mTorr (about 399 mPa), and high purity Ar gas was usedfor the electric discharge gas. The entire film thickness of the formedthird magnetic film was 10 nm.

The coercivity of the third magnetic film itself was 2 kOe (about 159.16kA/m), the perpendicular magnetic anisotropy energy was not less than4×10⁵ erg/cm³, and the saturation magnetization was 500 emu/ml.

Formation of Protective Film

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 76 on the third magnetic film 75 by means of theECR sputtering method. C was used for the target material, and Ar wasused for the electric discharge gas. The pressure during the sputteringwas 0.3 mTorr (about 399 mPa), and the introduced microwave electricpower was 0.7 kW. An RF bias voltage of 500 W was applied in order todraw the plasma excited by the microwave.

Measurement of Magnetic Characteristics

Thus, the magnetic recording medium having the stacked structure shownin FIG. 7 was manufactured, and magnetic characteristics of the obtainedmagnetic recording medium 70 were measured. An M-H loop was obtained bythe measurement with VSM (Vibration Sample Magnetometer). According tothe obtained results, the rectangularity ratios S, S* were 1.0. It wasrevealed that good rectangularity was obtained. The coercivity Hc was4.5 kOe (about 358.11 kA/m), and the saturation magnetization Ms was 300emu/cm³. It was revealed from the shape of the M-H loop that the firstto third magnetic films were subjected to exchange coupling. Theperpendicular magnetic anisotropy energy in the direction perpendicularto the substrate surface was 8×10⁶ erg/cm³. It was revealed that thelarge magnetic anisotropy was possessed in the direction perpendicularto the substrate surface. The volume of activation of the magnetic filmof the magnetic recording medium was measured to determine KuV/kT. As aresult, KuV/kT was 250. This fact indicates that the magnetic film ofthe magnetic recording medium is excellent in thermal stability.

Magnetic Recording Apparatus

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium 70, and thus the magnetic disk was completed. Aplurality of magnetic disks were manufactured in accordance with thesame process, and they were coaxially incorporated into the magneticrecording apparatus shown in FIGS. 2 and 3 in the same manner as in thefirst embodiment. The magnetic recording apparatus as described abovewas driven to record and reproduce information. During the recording andthe reproduction, the distance between the magnetic head surface and themagnetic film was maintained to be 12 nm. A signal (700 kFCI)corresponding to 40 Gbits/inch² was recorded on the magnetic disk toevaluate S/N of the disk. As a result, a reproduction output of 34 dBwas obtained.

Subsequently, a definite pattern was recorded on the magnetic disk, andthe fluctuation of the edge of the magnetic domain formed in themagnetic film was measured with a time interval analyzer. As a result ofthe measurement, the fluctuation was successfully reduced to be not morethan {fraction (1/10)} as compared with a magnetic disk provided with nofirst magnetic film. The error rate or defect rate of the magnetic diskwas measured. As a result, a value of not more than 1×10⁻⁵ was obtainedwhen no signal processing was performed. The magnetization state of therecorded portion was observed with a magnetic force microscope (MFM). Asa result, the zigzag pattern peculiar to the magnetization transitionarea was not observed. It is considered that the noise level wassuccessfully reduced thereby. The fact that the second magnetic film forrecording information is amorphous is also one of the causes tosuccessfully reduce the noise level.

In this embodiment, the perpendicularly magnetizable film based on theCo—Cr—Pt system was used as the first magnetic film to control the sizeand the position of the magnetic domain formed in the second magneticfilm. However, for example, a four-source system alloy or a five-sourcesystem alloy, which is obtained by adding, to the material as describedabove, Ta, Nb or the like to facilitate segregation of Cr at the Cograin boundary, may be used. In this case, the magnetic interactionbetween crystal grains is further reduced, and hence it is possible toimprove the positioning accuracy of the magnetic domain formed in thesecond magnetic film. The material, which is used for the magnetic filmof the magnetic wall movement type, is not suitable for the material forconstructing the first magnetic film. The material, in which the pinningsite for suppressing the movement of the magnetic wall exists and themagnetic interaction between magnetic grains is weakened, is preferablyused for the material for constructing the first magnetic film. It ispreferable that the direction of the anisotropy of the first magneticfilm is the same as that of the second magnetic film.

Materials other then those based on the Co alloy system may be also usedfor constructing the first magnetic film. For example, it is allowableto use a magnetic film such as a Co—CoO partially oxidized film and anamorphous alloy film of rare earth-iron family elements subjected togranulation into 10 nmφ. The granulation as described above makes itpossible to form the pinning site for the magnetic wall movement in themagnetic film.

In this embodiment, the amorphous ferrimagnetic film based on theTb—Fe—Co system was used for the second magnetic film. However, the sameor equivalent effect was also obtained, for example, even when Dy, Ho,or Gd was used in place of Tb. Among these elements, the largestperpendicular magnetic anisotropy is obtained with Tb. The magnitude ofthe perpendicular magnetic anisotropy is changed in an order ofDy>Ho>Gd. A plurality of rare earth elements may be combined in place ofthe construction of the rare earth element with only Tb. For example, itis allowable to use alloys composed of two elements such as Tb—Gd,Tb—Dy, Tb—Ho, Gd—Dy, Gd—Ho, and Dy—Ho, and alloys composed of three ormore elements. Accordingly, it is possible to control the perpendicularmagnetic anisotropy energy. It is preferable that the composition of therare earth element is not less than 20 at % and not more than 30 at % toform the perpendicularly magnetizable film, for the following reason.That is, when such a range is adopted, it is possible to obtain aferrimagnetic member having an easy axis of magnetization in thedirection perpendicular to the substrate surface.

The Fe—Co alloy was used as the transition metal. However, it is alsoallowable to use alloys such as Fe—Ni and Co—Ni. As for such alloys, theanisotropy energy is decreased in an order of Fe—Co>Fe—Ni>Co—Ni.

Eighth Embodiment

In this embodiment, a magnetic recording medium of the in-plane magneticrecording type was manufactured. The cross-sectional structure of themagnetic recording medium is the same as that of the magnetic recordingmedium shown in FIG. 1, having the structure in which an underlying basefilm 2, an information-recording film 3, a ferromagnetic film 4, and aprotective film 5 are successively stacked on a substrate 1. Theinformation-recording film 3 is composed of an artificial lattice filmof Er/Fe/Co, which is an in-plane magnetizable film having an easy axisof magnetization in a direction parallel to the substrate surface. Theferromagnetic film 4 is composed of a Co—Pt alloy film. A method forproducing the magnetic recording medium of the in-plane magneticrecording type will be explained below with reference to FIG. 1.

Formation of Underlying Base Film

At first, a glass substrate having a diameter of 2.5 inches (about 6.35cm) was prepared as the substrate 1. Subsequently, a silicon nitridefilm was formed as the underlying base film 2 to have a film thicknessof 10 nm on the substrate 1. The underlying base film 2 is a layer whichis provided in order to improve the protection of theinformation-recording film 3 and the adhesive performance with respectto the substrate 1. The magnetron sputtering method was used to form theunderlying base film 2. Si₃N₄ was used for the target, and Ar was usedfor the electric discharge gas. The electric discharge gas pressure was10 mTorr (about 1.33 Pa), and the introduced RF electric power was 1kW/150 mmφ.

Formation of Information-Recording Film

Subsequently, the information-recording film 3 was formed on theunderlying base film 2. The information-recording film 3 is anartificial lattice film obtained by periodically stacking thin filmseach having a three-layered structure composed of an Er layer, an Felayer, and a Co layer. The film thickness of each of the layers of thethin film having the three-layered structure is Fe (1 nm)/Co (0.1 nm)/Er(0.2 nm). The multi-source co-sputtering method based on three sourcesof Er, Fe, and Co was used as a method for forming theinformation-recording film (artificial lattice film) 3 as describedabove. The film thickness of each of the layers of the thin film havingthe three-layered structure can be precisely controlled to have adesired value by combining the velocity of revolution of the substrateand the electric power introduced during the sputtering. In this case,the introduced DC electric power was 0.3 kW during the formation of theEr film, it was 0.15 kW during the formation of the Co film, and it was0.7 kW during the formation of the Fe film. The number of revolutions ofthe substrate was 30 rpm. High purity Ar gas was used for the electricdischarge gas. The electric discharge gas pressure during the sputteringwas 3 mTorr (about 399 mPa). The artificial lattice film(information-recording film), which had the structure comprising theperiodically stacked three-layered thin films of Fe (1 nm)/Co (0.1nm)/Er (0.2 nm), was formed to have a film thickness of about 20 nmunder the sputtering condition as described above.

The gas pressure during the sputtering affects the magnetic interactionbetween magnetic clusters. When the sputtering is performed under thecondition in which the gas pressure is high, a film having smallmagnetic interaction is obtained. Such a film is preferred as a film formagnetic recording. However, the optimum gas pressure differs dependingon the film formation apparatus to be used. The gas pressure is adjusteddepending on the film formation apparatus. It is considered that thedifference in gas pressure depending on the film formation apparatus iscaused by the difference in cathode structure of the target and thedifference in gas flow in the vacuum chamber or tank.

When the artificial lattice film as described above is formed as thefilm, the degree of vacuum at the initial evacuation is important. Inthis embodiment, the film was formed after effecting the evacuation upto 4×10⁻⁹ Torr (about 532×10⁻⁹ Pa). The numerical values, which areadopted in this embodiment when the information-recording film 3 isformed, are not absolute, which change depending on, for example, thesystem of the sputtering. When the information-recording film 3 isconstructed as the artificial lattice film as described above, then itis possible to increase the in-plane magnetic anisotropy energy in thedirection parallel to the substrate as compared with a case in which anamorphous alloy film of Er—Fe—Co is used as an information-recordingfilm, and it is possible to improve the thermal stability of theinformation-recording film. The magnetization of theinformation-recording film 3 as described above lies in the differencebetween the magnetization of the transition metal and the magnetizationof the rare earth element. This embodiment was designed so that themagnetization of the transition metal was dominant as compared with themagnetization of the rare earth element.

Formation of Ferromagnetic Film

Subsequently, a Co₅₅Pt₄₅ film was formed as the ferromagnetic film 4 onthe information-recording film 3. The ferromagnetic film 4 was formed tohave a film thickness of 10 nm so that the magnetic exchange interactionwas generated with respect to the information-recording film 3. Therange of the film thickness of the ferromagnetic film, in which theexchange coupling force is exerted with respect to theinformation-recording film 3, is 15 nm at the maximum in thisembodiment. When the ferromagnetic film 4 was formed, the film wascontinuously formed without breaking the vacuum during the process afterforming the Er/Fe/Co artificial lattice film as theinformation-recording film 3 in order to generate the magnetic coupling.

The Co—Pt film as the ferromagnetic film 4 does not exhibit satisfactorymagnetization unless crystallization is effected. For this reason, theECR sputtering method was used. As for the conditions for thesputtering, the pressure during the sputtering was 0.3 mTorr (about 39.9mPa), and the introduced microwave electric power was 0.7 kW. In orderto draw the plasma excited by the microwave, a DC bias voltage of 500 Vwas applied. Ar was used for the sputtering gas.

When the ECR sputtering method is used, the film can be formed at a lowtemperature without raising the substrate temperature. Therefore, it ispossible to suppress the interlayer diffusion which would be otherwisecaused with respect to the Er/Fe/Co artificial lattice film. If suchinterlayer diffusion takes place, it is especially feared that theperpendicular magnetic anisotropy energy may be lowered and thecoercivity may be lowered. In view of the production, it is preferablethat the value of the anisotropy energy is stable. Therefore, it ispreferable that the film is formed so that the interlayer diffusion isreduced. Further, the decrease in coercivity due to the interlayerdiffusion causes the decrease in reproduced signal output and thedecrease in reliability. Also from this viewpoint, it is desirable toreduce the interlayer diffusion. Therefore, it is desirable that thesubstrate temperature is low during the film formation. The ECRsputtering method as described above is effective to form the film witha material which requires the heat treatment in order to express themagnetization, as in the Co—Pt-based magnetic film as the ferromagneticfilm 4. The ECR sputtering method is preferred as a film formationmethod for forming a thin film (or a multilayered film) in an order ofnanometer (nm).

Formation of Protective Film

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 5 on the ferromagnetic film 4. The ECR sputteringmethod based on the use of the microwave was used for the filmformation. C (carbon) was used for the target material, and Ar was usedfor the electric discharge gas. The pressure during the sputtering was0.3 mTorr (about 39.9 mPa), and the introduced microwave electric powerwas 0.5 kW. A DC bias voltage of 500 V was applied in order to draw theplasma excited by the microwave. The quality of the carbon film greatlydepends on the sputtering conditions as described above and theelectrode structure. Therefore, the conditions are not absolute. Thus,the magnetic recording medium having the stacked structure shown in FIG.1 was obtained.

Subsequently, magnetic characteristics of the manufactured magneticrecording medium were measured. According to an M-H loop obtained withVSM, both of the rectangularity ratios S, S* were 1.0, exhibiting goodrectangularity. The coercivity Hc was 3.9 kOe (about 310.362 kA/m). Asfor the magnetic anisotropy energy of the information-recording film,the in-plane magnetic anisotropy energy in the direction parallel to thesubstrate surface was 3×10⁶ erg/cm³.

Subsequently, the volume of activation of the magnetic recording mediumwas measured in accordance with the same method as used in the firstembodiment. As a result of the measurement of the volume of activation,the volume of activation of the information-recording film of themagnetic recording medium of this embodiment was extremely large, i.e.,about fifty times the value of a Co—Cr—Pt-based magnetic film widelyused as the magnetic recording medium. This fact indicates that theinformation-recording film of this embodiment has small thermalfluctuation and small thermal demagnetization, and it is excellent inthermal stability.

Subsequently, the saturation magnetization was measured for theinformation-recording film 3 and the ferromagnetic film 4. Thesaturation magnetization of the ferromagnetic film 4 based on the Co—Ptsystem was 600 emu/cm³ which was a value larger than that of thesaturation magnetization of 380 emu/cm³ of the information-recordingfilm 3. It was revealed by the measurement with VSM that the exchangecoupling force between the information-recording film 3 and theferromagnetic film 4 was strong, and the information-recording film 3and the ferromagnetic film 4 magnetically behaved as a monolayer film.As described above, the reason why the material having the saturationmagnetization larger than that of the information-recording film 3 isused for the ferromagnetic film 4 is that it is intended to increase,with the ferromagnetic film 4, the magnetic flux coming from themagnetic domain formed in the information-recording film 3. Accordingly,when the magnetic recording medium is subjected to reproduction by usingthe magnetic head, a large reproduction output is obtained.

Subsequently, the organizations and the structures of theinformation-recording film 3 and the ferromagnetic film 4 wereinvestigated by means of a high resolution transmission electronmicroscope. As a result, no distinct lattice was found. According tothis fact, it was revealed that any one of the information-recordingfilm 3 and the ferromagnetic film 4 was amorphous or aggregates ofextremely fine organizations. Especially, it was revealed that theinformation-recording film 3 was the artificial lattice film having adesired film thickness composed of thin films of the three-layeredstructure of Fe (1 nm)/Co (0.1 nm)/Er (0.2 nm). The film thicknesses ofthe respective layers of the thin film having the three-layeredstructure were well coincident with the measured values obtained withthe X-ray.

Subsequently, a lubricant was applied onto the protective film 5, andthus the magnetic disk was completed. A plurality of magnetic disks weremanufactured in accordance with the same process, and they werecoaxially incorporated into the magnetic recording apparatus constructedin the same manner as in the first embodiment (see FIGS. 2 and 3). Themagnetic recording apparatus was driven, and a signal (700 kFCI)corresponding to 40 Gbits/inch² (6.20 Gbits/cm²) was recorded on themagnetic disk to evaluate S/N of the disk. As a result, a reproductionoutput of 34 dB was obtained. The error rate or defect rate of themagnetic disk was measured. As a result, a value of not more than 1×10⁻⁵was obtained when no signal processing was performed.

The magnetization state of the recorded portion (recording magneticdomain) was observed with a magnetic force microscope (MFM). As a resultof the observation, the zigzag pattern peculiar to the magnetizationtransition area was not observed. FIG. 9 schematically shows a situationof the magnetization state of the recorded portion. FIG. 9 alsoschematically shows a situation of the magnetization state of a recordedportion of an information-recording film when the recording wasperformed in the same manner as described above with a conventionalmagnetic recording medium (Comparative Example) provided with aninformation-recording film based on the Co—Cr—Pt system for the purposeof comparison. It is considered that the noise level is extremely smallas compared with the magnetic recording medium (Comparative Example)provided with the information-recording film based on the Co—Cr—Ptsystem, because the zigzag pattern peculiar to the magnetizationtransition area scarcely exists in the magnetic recording medium of theembodiment of the present invention. Further, it is considered that thelow noise level is also caused by the fact that theinformation-recording film is the aggregate of fine and minute grains.Further, in the case of the magnetic recording medium of the embodimentof the present invention, the minute inverse magnetic domain wasscarcely observed in the recording magnetic domains and between themutually adjoining recording magnetic domains. One of the causes of thelow noise level is also this fact.

This embodiment is illustrative of the case in which the Er/Fe/Co systemis used for the artificial lattice film for constructing theinformation-recording film. However, the same or equivalentcharacteristics were also obtained when another rare earth element suchas La, Ce, Pr, Nd, Sm, Eu, Tm, Yb, Lu, or Y was used in place of Er.Especially, a magnetic recording film, which was constructed with Ce,Pr, Nd, Sm, Tm, or Yb, exhibited preferred magnetic characteristics nextto those of the magnetic recording film constructed with Er.Alternatively, the rare earth elements for constructing the artificiallattice film may be constructed with an alloy composed of two elementsrepresented by Er—Pr, Er—Nd, Er—Sm, and Er—Tm. The two-layered film ofFe/Co comprising the thin film composed of Fe and the thin film composedof Co was used as the transition metal film for constructing theartificial lattice film. However, the artificial lattice film may bealso constructed with a monolayer film composed of an alloy such asFe—Co, Fe—Ni, and Co—Ni.

The underlying base film 2 is not necessarily formed in the stackedstructure shown in FIG. 1. It is also possible to form a control filmfor controlling the movement of the magnetic wall of the recordingmagnetic domain formed in the information-recording film, in place ofthe underlying base film 2 as described above. The underlying base film2 may be formed as a film in accordance with the reactive sputteringmethod by using Si as the target and Ar/N₂ as the electric dischargegas. A film of oxide such as silicon oxide, nitride (for example,aluminum nitride) other than silicon nitride, and oxynitride such asSi—Al—O—N may be used for the underlying base film other than siliconnitride.

The information-recording film has been formed by means of the DCmagnetron sputtering method. However, in the present invention, thesputtering method (ECR sputtering method) based on the use of theelectron cyclotron resonance and the RF magnetron sputtering method maybe used.

In this embodiment, the Co—Pt system was used for the ferromagneticfilm. However, a ferromagnetic film based on, for example, the Co—Cr—Tasystem, the Co—Cr—Pt system, or the Co—Cr—Pt—Ta system may be used.Alternatively, it is also allowable to use an alloy such as Co—Pd andCo—Rh and an alternately stacked multilayered film (artificial latticefilm) such as Co/Pt, Co/Pd, and Co/Rh. The reason why the Co-basedmaterial is used for the ferromagnetic film in this embodiment is thatsuch a material has the large saturation magnetization as compared withan Fe-based material.

Ninth Embodiment

In this embodiment, a magnetic recording medium of the in-plane magneticrecording type was manufactured. The cross-sectional structure of themagnetic recording medium is the same as that of the magnetic recordingmedium shown in FIG. 7. The magnetic recording medium has a structure inwhich an underlying base film 72, a first magnetic film 73, a secondmagnetic film 74, a third magnetic film 75, and a protective film 76 aresuccessively stacked on a substrate 71. With reference to FIG. 7, thefirst magnetic film 73 is a layer for suppressing the movement of themagnetic wall formed in the second magnetic film, and it is constructedwith a Co—Cr—Pt film. The second magnetic film 74 is a layer forrecording information therein, and it is constructed with an Er—Fe—Cofilm. The third magnetic film 75 is a layer for enhancing the reproducedsignal output during reproduction, and it is constructed with a Pt—Coalloy film. A method for producing the magnetic recording medium 70 willbe explained below.

Formation of Underlying Base Film

At first, a glass substrate having a diameter of 2.5 inches (about 6.35cm) was prepared as the substrate 71. A Cr₈₅Ti₁₅ alloy film was formedas the underlying base film 72 on the substrate 71 by means of the DCmagnetron sputtering method. The underlying base film 72 is capable ofcontrolling the orientation of the first magnetic film 73. A Cr—Ti alloywas used for the target material, and pure Ar was used for the electricdischarge gas. The pressure during the sputtering was 3 mTorr (about 399mPa), and the introduced DC electric power was 1 kW/150 mmφ. Thesputtering was performed at the room temperature.

Formation of First Magnetic Film

Subsequently, a magnetic film composed of CO₆₉Cr₁₉Pt₁₂ was formed as thefirst magnetic film 73 on the underlying base film 72 by means of the DCsputtering method. A Co—Cr—Pt alloy was used for the target material,and pure Ar was used for the electric discharge gas. The pressure duringthe sputtering was 30 mTorr (about 3.99 Pa), and the introduced DCelectric power was 1 kW/150 mmφ. The substrate temperature during thefilm formation was room temperature. Magnetic characteristics of thesingle first magnetic film were investigated. As a result, thecoercivity was 2.5 kOe (about 198.95 kA/m), and the saturationmagnetization was 360 emu/ml.

Formation of Second Magnetic Film

Subsequently, an amorphous film of Er—Fe—Co was formed as the secondmagnetic film 74 on the first magnetic film 73. The composition of thesecond magnetic film 74 is Er₁₉Fe₇₁Co₁₀, which is a composition in whichthe sub-lattice magnetization of the transition metal is dominant. Thesecond magnetic film 74 was formed by using the RF magnetron sputteringmethod. In the sputtering, an Er—Fe—Co alloy was used for the targetmaterial, and pure Ar was used for the electric discharge gas. Theformed second magnetic film 74 has a film thickness of 20 nm. Thepressure during the sputtering is 3 mTorr (about 399 mPa), and theintroduced RF electric power is 1 kW/150 mmφ. In this embodiment, thefilm was formed by using the RF magnetron sputtering method. However,the DC magnetron sputtering method may be used.

The coercivity of the obtained second magnetic film 74 was 3.8 kOe(about 302.404 kA/m), and the saturation magnetization was 450 emu/ml.The in-plane magnetic anisotropy energy was not less than 7×10⁶ erg/cm³.The film was a magnetic member having the magnetic anisotropy in thedirection parallel to the substrate surface.

Third Magnetic Film

Subsequently, an alloy film of Pt₂₀Co₈₀ was formed as the third magneticfilm 75 on the second magnetic film 74 by using the RF magnetronsputtering method in the same manner as in the formation of the secondmagnetic film. The third magnetic film 75 is a layer which is providedin order to improve the reproduction characteristics. The electricdischarge gas pressure during the sputtering is 3 mTorr (about 399 mPa),and the introduced RF electric power is 1 kW/150 mmφ. The film thicknessof the third magnetic film 75 was 5 nm. There is a certain limit for therange in which the exchange coupling force from the second magnetic film74 is exerted. The film thickness of the third magnetic film 75 is 15 nmat the maximum, in order to reliably exert the exchange coupling forcefrom the second magnetic film 74 on the third magnetic film 75. Magneticcharacteristics of the third magnetic film 75 as described above weremeasured. As a result, the coercivity was 1 kOe (about 79.58 kA/m), andthe saturation magnetization was 560 emu/ml.

Formation of Protective Film

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 76 on the third magnetic film 75 by means of theECR sputtering method. C was used for the target material, and Ar wasused for the electric discharge gas. The pressure during the sputteringwas 0.3 mTorr (about 39.9 mPa), and the introduced microwave electricpower was 0.5 kW. A DC bias voltage of 500 V was applied in order todraw the plasma excited by the microwave.

Measurement of Magnetic Characteristics

Thus, the magnetic recording medium having the stacked structure shownin FIG. 7 was manufactured, and magnetic characteristics of the obtainedmagnetic recording medium were measured. An M-H loop was obtained by themeasurement with VSM (Vibration Sample Magnetometer). According to theobtained results, the rectangularity ratios S, S* were 1.0. It wasrevealed that good rectangularity was obtained. The coercivity Hc was3.5 kOe (about 278.53 kA/m), and the saturation magnetization Ms was 450emu/cm³. The in-plane magnetic anisotropy energy in the directionparallel to the substrate surface was 4×10⁵ erg/cm³. It was revealedthat the large magnetic anisotropy was possessed in the directionparallel to the substrate surface. The volume of activation of themagnetic film of the magnetic recording medium was measured to determinethe value of KuV/kT. As a result, the value was 350. The value waslarger than the value (about 60 to 120) of a magnetic film based on theCo—Cr—Pt system widely used as the conventional magnetic recordingmedium. This fact indicates that the magnetic film of the magneticrecording medium is excellent in thermal stability.

Magnetic Recording Apparatus

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium, and thus the magnetic disk was completed. A pluralityof magnetic disks were manufactured in accordance with the same process,and they were coaxially incorporated into the magnetic recordingapparatus shown in FIGS. 2 and 3 in the same manner as in the firstembodiment. The magnetic recording apparatus as described above was usedto record and reproduce information. During the recording and thereproduction, the distance between the magnetic head surface and themagnetic film was maintained to be 12 nm. A signal (700 kFCI)corresponding to 40 Gbits/inch² was recorded on the magnetic disk toevaluate S/N of the disk. As a result, a reproduction output of 36 dBwas obtained. The recording was performed in the same manner asdescribed above on a magnetic disk having no Co—Cr alloy (third magneticfilm) to reproduce recorded information. As a result, a reproductionoutput of 34 dB was obtained, which was smaller than the above by 2 dB.

Subsequently, a definite pattern was recorded on the magnetic disk, andthe fluctuation of the edge of the magnetic domain formed in themagnetic film was measured with a time interval analyzer. As a result ofthe measurement, the fluctuation was successfully reduced to be not morethan {fraction (1/10)} as compared with a magnetic disk provided with nofirst magnetic film. According to this result, it was revealed that thejitter, which would be generated resulting from the movement of themagnetic wall in the second magnetic film during the recording ofinformation to fluctuate the position of the recording magnetic domain,was successfully reduced by providing the first magnetic film. The errorrate or defect rate of the magnetic disk was measured. As a result, avalue of not more than 1×10⁻⁵ was obtained when no signal processing wasperformed.

The magnetization state of the recorded portion was observed with amagnetic force microscope (MFM). As a result, the zigzag patternpeculiar to the magnetization transition area was not observed.Accordingly, the noise level was successfully reduced thereby ascompared with a conventional magnetic recording medium based on theCo—Cr—Pt system. The fact that the second magnetic film for recordinginformation is amorphous is also one of the causes to successfullyreduce the noise level.

In this embodiment, the magnetic film based on the Co—Cr—Pt system wasused as the first magnetic film to control the size and the position ofthe magnetic domain formed in the second magnetic film. However, forexample, a four-source system alloy or a five-source system alloy, whichis obtained by adding Ta, Nb or the like to the material as describedabove, may be used. Pd or Rh may be used other than Pt. For example, anelement such as P, B, or Si may be added by 2 to 3% in view of thecorrosion resistance and the realization of fine and minute magneticgrains.

In this embodiment, the amorphous ferrimagnetic film based on theEr—Fe—Co system was used for the second magnetic film. However, the sameor equivalent effect is also obtained, for example, even when La, Ce,Pr, Nd, Pm, Sm, Eu, Tm, Yb, Lu, or Y is used in place of Er. Forexample, it is possible to use an amorphous ferrimagnetic material suchas Tb—Fe—Co, Dy—Fe—Co, Ho—Fe—Co, and Gd—Fe—Co. In place of the use ofonly Er for the rare earth element for constructing the second magneticfilm, it is also allowable to use an alloy constructed by combining aplurality of rare earth elements such as alloys containing two elementsand alloys containing three or more elements. Specifically, the secondmagnetic film may be constructed with a ferrimagnetic film such asTb—Dy—Fe—Co, Tb—Gd—Fe—Co, Tb—Ho—Fe—Co, Gd—Ho—Fe—Co, Gd—Dy—Fe—Co, andDy—Ho—Fe—Co. For example, the vacuum vapor deposition method and thesputtering method such as the DC magnetron sputtering method and the RFmagnetron sputtering method can be used to form the ferrimagneticamorphous film. The Fe—Co alloy, was used as the transition metal.However, an alloy such as Fe—Ni and Co—Ni may be used.

The Pt—Co alloy was used for the third magnetic film. However, anelement such as Pd and Rh may be used in place of Pt. An alloy composedof two elements such as Pt—Pd, Pt—Rh, and Pd—Rh may be used.Alternatively, Ni can be also used in place of Co. Furtheralternatively, Fe may be used in place of Co. In this case, it ispreferable to adopt a composition area in which the saturationmagnetization larger than that of the first magnetic film is obtained.Further, there is no limitation to the alloy of Pt and Co. The same orequivalent effect is also obtained even in the case of an alternatelystacked multilayered film (artificial lattice film) constructed byalternately stacking layers based on the Pt system and layers based onthe Co system.

Tenth Embodiment

In this embodiment, a magnetic recording medium having a cross-sectionalstructure as shown in a schematic sectional view in FIG. 8 wasmanufactured as the magnetic recording medium according to the secondaspect of the present invention. The magnetic recording medium 80 hasthe structure in which an underlying base film 82, a magnetic film(information-recording film) 83, and a protective film 84 aresuccessively stacked on a substrate 81. A method for producing themagnetic recording medium 80 will be explained below.

Preparation of Substrate

At first, a glass substrate having a diameter of about 2.5 inches (about6.35 cm) was prepared as the substrate 81. The substrate used in thisembodiment is an example. A disk substrate having any size may be used,and a metal substrate such as Al or Al alloy may be used. The effect ofthe present invention is not affected by the material quality and thesize of the substrate to be used. Further, it is also allowable to use asubstrate comprising an NiP layer formed on a substrate of glass, Al, orAl alloy by means of the plating method or the sputtering method.

Formation of underlying Base Film

Subsequently, a silicon nitride film was formed as the underlying basefilm 82 having a film thickness of 50 nm on the substrate 81 by means ofthe RF magnetron sputtering method. The underlying base film 82 makes itpossible to improve the adhesive performance between the substrate 81and the magnetic film 83. Silicon was used for the target material, andan Ar—N₂ mixed gas (Ar/N₂ partial pressure ratio: 90/10) was used forthe electric discharge gas. The pressure during the sputtering was 3mTorr (about 399 mPa), and the introduced RF electric power was 1 kW/150mmφ. The sputtering was performed at the room temperature.

The underlying base film 82 has the function as the nucleation site(position to serve as the core upon the formation of magnetic domain)when a magnetic field is applied from the outside to the magnetic film83 to form the magnetic domain, and it has the effect as the obstaclefor the magnetic wall movement. Such an effect not only depends on thematerial for constructing the underlying base film 82 but also dependson the condition for the film formation. The material for the underlyingbase film 82 is not limited to silicon nitride as well. It is alsoallowable to use a metal film such as Ni—P, Al, Al—Cr alloy, Al—Tialloy, Cr, and Cr—Ti alloy. Alternatively it is also allowable to use aninorganic compound such as AlN, Zro₂, and BN.

Formation of Magnetic Film

Subsequently, an amorphous film of Tb—Fe—Co was continuously formed asthe magnetic film 83 on the underlying base film 82 without breaking thevacuum after the formation of the underlying base film 82. Thecomposition of the magnetic film 83 is Tb₁₇Fe₇₄CO₉, in which thesub-lattice magnetization of the transition metal is dominant. The RFmagnetron sputtering method was used for the formation of the magneticfilm 83. In the sputtering, a Tb—Fe—Co alloy was used for the targetmaterial, and Ar-O₂ mixed gas (partial pressure ratio: 98/2) was usedfor the electric discharge gas. The thickness of the formed magneticfilm 83 is 20 nm. The electric discharge gas pressure during thesputtering was 10 mTorr (about 1.33 Pa), and the introduced RF electricpower was 1 kW/150 mmφ.

The coercivity of the obtained magnetic film 83 was 3.5 kOe (about278.53 kA/m), the saturation magnetization was 250 emu/ml, and theperpendicular magnetic anisotropy energy was 5×10⁶ erg/cm³.

Formation of Protective Film

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 84 on the magnetic film 83 by means of the ECRsputtering method. C was used for the target material, and Ar was usedfor the electric discharge gas. The pressure during the sputtering was0.3 mTorr, and the introduced microwave electric power was 0.7 kW. An RFbias voltage of 500 W was applied in order to draw the plasma excited bythe microwave. The hardness of the manufactured protective film 84 wasmeasured with a hardness tester produced by Hysitron. As a result, thehardness was 21 GPa. According to a result obtained by the Ramanspectroscopy, it was revealed that the sp3 bond played a key role.

When the protective film 84 was formed, Ar was used for the sputteringgas. However, the film may be formed with a gas containing nitrogen.When the gas containing nitrogen is used, then the grains become fineand minute, the obtained C film is densified, and it is possible tofurther improve the protective performance. As described above, the filmquality of the protective film greatly depends on the sputteringcondition and the electrode structure. Therefore, the conditionsdescribed above are not absolute. It is desirable that the conditionsare appropriately adjusted depending on the apparatus to be used.

Measurement of Magnetic Characteristics

Thus, the magnetic recording medium 80 having the stacked structureshown in FIG. 8 was manufactured, and magnetic characteristics of theobtained magnetic recording medium 80 were measured. An M-H loop wasobtained by the measurement with VSM (Vibration Sample Magnetometer).According to the obtained results, the rectangularity ratios S, S* were1.0. It was revealed that good rectangularity was obtained. Thecoercivity Hc was 3.5 kOe (about 278.53 kA/m), and the saturationmagnetization Ms was 250 emu/cm³. The perpendicular magnetic anisotropyenergy in the direction perpendicular to the substrate surface was 3×10⁶erg/cm³. The volume of activation of the magnetic film of the magneticrecording medium was measured to determine the value of KuV/kT. As aresult, the value was 280. This fact indicates that the magnetic film ofthe magnetic recording medium is excellent in thermal stability.

Subsequently, the cross-sectional structure of the magnetic film of themagnetic recording medium was analyzed by means of the Auger electronspectroscopy. As a result of the analysis, it was revealed that oxygenexisted uniformly in the magnetic film. The content of oxygen in themagnetic film was determined by means of ESCA. As a result, the contentof oxygen was 10 at %. The planar structure of the magnetic film wasobserved with a transmission electron microscope (TEM). As a result,grains of Tb oxide of about 3 nm were present at a rate of one grain ina square of 100 nm. The cross-sectional structure of the magnetic filmwas observed. As a result, it was revealed that the grains were presentin a dispersed manner randomly three-dimensionally.

Magnetic Recording Apparatus

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium, and thus the magnetic disk was completed. A pluralityof magnetic disks were manufactured in accordance with the same process,and they were coaxially incorporated into the magnetic recordingapparatus constructed in the same manner as in the first embodiment (seeFIGS. 2 and 3).

The magnetic recording apparatus was driven so that a signal (700 kFCI)corresponding to 40 Gbits/inch² (about 6.20 Gbits/cm²) was recorded onthe magnetic disk to evaluate S/N of the magnetic disk. As a result, areproduction output of 34 dB was obtained. The signal was recorded inthe same manner as described above on a magnetic recording mediumcontaining substantially no oxygen in a magnetic film to evaluate S/N.As a result, the noise was increased by about 5 dB over the entirefrequency area. Thus, the effect to reduce the noise was obtained bycontaining oxygen in the magnetic film as described above.

Subsequently, a definite pattern was recorded on the magnetic disk ofthe present invention, and the fluctuation of the edge of the magneticdomain formed in the magnetic film was measured with a time intervalanalyzer. As a result of the measurement, the fluctuation wassuccessfully reduced to be not more than {fraction (1/10)} as comparedwith a conventional magnetic disk containing substantially no oxygen ina magnetic film. Further, the fluctuation of the edge of the magneticdomain was measured in accordance with the same method for magneticdisks manufactured by changing the concentration of oxygen contained inthe magnetic film to have a variety of values. As a result, the effectto reduce the fluctuation of the edge appeared in the magnetic diskprovided with the magnetic film having an oxygen concentration of 0.1 at%. In the case of the magnetic disks having the oxygen concentrations(contents of oxygen) in the magnetic films of 0.1 at % to 5 at %, thefluctuation of the edge was reduced to be not more than ½ as comparedwith the conventional magnetic disk. In the case of the magnetic diskshaving the oxygen concentrations in the magnetic films of 5 at % to 10at %, the fluctuation of the edge was reduced to be ⅓ to ¼. Further, inthe case of the magnetic disks having the oxygen concentrations in themagnetic films of 10 at % to 20 at %, the fluctuation of the edge wasreduced to be {fraction (1/10)}, and the magnetic disks exhibitedextremely satisfactory characteristics. In the case of the magneticdisks having the oxygen concentrations in the magnetic films exceeding20 at %, the perpendicular magnetic anisotropy energy of the magneticfilm was suddenly decreased, and the disks did not exhibit theperpendicular magnetization. The error rate or defect rate of themagnetic disk was measured. As a result, a value of not more than 1×10⁻⁵was obtained when no signal processing was performed. The magnetizationstate of the recorded portion was observed with a magnetic forcemicroscope (MFM). As a result, the zigzag pattern peculiar to themagnetization transition area was not observed. It is considered thenoise level was successfully reduced thereby.

In this embodiment, the oxide of Tb was formed by adding oxygen into themagnetic film. However, the same or equivalent effect can be alsoobtained even when nitride of Tb is formed by adding nitrogen in placeof oxygen. The corrosion resistance of the magnetic film was greatlyimproved by adding nitrogen, probably for the following reason. That is,it is considered that a part of nitrogen formed solid solution in Fe.

In this embodiment, the amorphous ferrimagnetic film based on theTb—Fe—Co system was used for the magnetic film. However, the same orequivalent effect was also obtained, for example, even when Dy, Ho, orGd was used in place of Tb. Among these elements, the largestperpendicular magnetic anisotropy is obtained with Tb. The magnitude ofthe perpendicular magnetic anisotropy is changed in an order ofDy>Ho>Gd. A plurality of rare earth elements may be combined in place ofthe construction of the rare earth element with only Tb. For example, itis allowable to use alloys composed of two elements such as Tb—Gd,Tb—Dy, Tb—Ho, Gd—Dy, Gd—Ho, and Dy—Ho, and alloys composed of three ormore elements. Accordingly, it is possible to control the perpendicularmagnetic anisotropy energy. It is preferable that the composition of therare earth element is not less than 20 at % and not more than 30 at % toform the perpendicularly magnetizable film, for the following reason.That is, when such a range is adopted, it is possible to obtain aferrimagnetic member having an easy axis of magnetization in thedirection perpendicular to the substrate surface.

The Fe—Co alloy was used as the transition metal. However, it is alsoallowable to use alloys such as Fe—Ni and Co—Ni. As for such alloys, theanisotropy energy is decreased in an order of Fe—Co>Fe—Ni>Co—Ni.

Eleventh Embodiment

In this embodiment, a magnetic recording medium having the same stackedstructure as that of the magnetic recording medium manufactured in thetenth embodiment (see FIG. 8) was manufactured except that a magneticfilm was constructed with an artificial lattice film of Tb/Fe/Co. Themethod for forming those other than the magnetic film is the same asthat used in the tenth embodiment, explanation of which is omitted. Amethod for forming the magnetic film (Tb/Fe/Co artificial lattice film)will be explained below.

Method for Forming Magnetic Film

When the magnetic film 83 was formed, the multi-source co-sputteringmethod based on three sources of Tb, Fe, and Co was used. The filmthickness of each of the layers is Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm).The film thickness of each of the layers can be precisely controlled tohave a desired value by combining the velocity of revolution of thesubstrate and the electric power introduced during the sputtering. Inthis embodiment, the introduced DC electric power was set to be 0.3 kWfor Tb, 0.15 kW for Co, and 0.7 kW for Fe. The number of revolutions ofthe substrate was 30 rpm. The electric discharge gas pressure during thesputtering was 3 mTorr. A mixed gas of Ar—N₂ was used for the electricdischarge gas. Thus, the artificial lattice film was formed to have anentire thickness of about 40 nm by periodically stacking stacked unitseach composed of Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm).

When the artificial lattice film as described above is manufactured, thedegree of vacuum at the initial evacuation is important. In thisembodiment, the film was manufactured after effecting the evacuation upto 4×10⁻⁹ Torr. The values as described above are not absolute, whichchange depending on, for example, the system of the sputtering. In thisembodiment, the film was manufactured by means of the DC magnetronsputtering method. However, the film formation may be carried out byusing the RF magnetron sputtering method and the sputtering method (ECRsputtering method) based on the use of the electron cyclotron resonance.

When the artificial lattice film is used for the magnetic film asdescribed above, then it is possible to increase the perpendicularmagnetic anisotropy energy as compared with a case in which an amorphousalloy film based on the Tb—Fe—Co system is used as a magnetic film, andit is possible to improve the thermal stability of the magnetic film.The magnetic film exhibits substantially the same magneticcharacteristics as those of the ferrimagnetic member composed of atransition metal such as Fe and Co and a rare earth element such as Tb.The magnetization of such a magnetic film appears as the differencebetween the magnetization of the transition metal thin film layer andthe magnetization of the rare earth element thin film layer. Themagnetic film manufactured in this embodiment is a magnetic film inwhich the magnetization of the transition metal is dominant. A part ofnitrogen in the mixed gas was present in Co of the formed magnetic film,because the Ar—N₂ mixed gas was used when the magnetic film was formed.

Measurement of Magnetic Characteristics

Subsequently, magnetic characteristics of the magnetic recording mediumprovided with the artificial lattice film as described above as themagnetic film were measured. An M-H loop was obtained by the measurementwith VSM (vibration Sample Magnetometer). According to the obtainedresults, both of the rectangularity ratios S, S* were 1.0. It wasrevealed that good rectangularity was obtained. The coercivity Hc was3.5 kOe (about 278.53 kA/m). As for the magnetic anisotropy energy ofthe magnetic film, the perpendicular magnetic anisotropy energy in thedirection perpendicular to the substrate surface was 5×10⁶ erg/cm³. Thevolume of activation V of the magnetic recording medium was measured todetermine the value of KuV/kT as the index for the thermal stability ofthe magnetic layer. As a result, the value of KuV/kT was 400. This factindicates that the magnetic film is formed of a material which isexcellent in thermal stability with small thermal fluctuation and smallthermal demagnetization.

Further, the magnetic film was observed with a high resolutiontransmission electron microscope (TEM). As a result, it was revealedthat the artificial lattice film was provided, in which the stackedunits each composed of Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm) wereperiodically stacked to give the desired film thickness.

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium, and thus the magnetic disk was completed. A pluralityof magnetic disks were manufactured in accordance with the same process,and they were coaxially incorporated into the magnetic recordingapparatus shown in FIGS. 2 and 3 in the same manner as in the firstembodiment. The magnetic recording apparatus as described above was usedto record and reproduce information. During the recording and thereproduction, the distance between the magnetic head surface and themagnetic film was maintained to be 12 nm. A signal (700 kFCI)corresponding to 40 Gbits/inch² was recorded on the magnetic disk toevaluate S/N of the disk. As a result, a reproduction output of 36 dBwas obtained. The error rate or defect rate of the magnetic disk wasmeasured. As a result, a value of not more than 1×10⁻⁵ was obtained whenno signal processing was performed.

This embodiment is illustrative of the case in which the artificiallattice film based on the Tb/Fe/Co system is used. However, the same orequivalent effect is obtained even when one element of Gd, Dy, and Ho isused other than Tb, or even when an alloy such as Gd—Tb, Gd—Dy, Gd—Ho,Tb—Dy, and Tb—Ho is used. The artificial lattice film was constructed byusing the two-layered film of Fe/Co as the transition metal. However, itis also possible to obtain a magnetic film having equivalentcharacteristics by using an alternately stacked multilayered filmcomposed of an alloy such as Fe—Co, Fe—Ni, and Co—Ni and a rare earthelement such as Tb.

Twelfth Embodiment

In this embodiment, a magnetic recording medium having the same stackedstructure as that of the magnetic recording medium manufactured in thetenth embodiment (see FIG. 8) was manufactured except that a magneticfilm was constructed by alternately stacking layers containing oxygenand layers containing no oxygen. The method for forming the film otherthan the magnetic film is the same as that used in the tenth embodiment,explanation of which is omitted. A method for forming the magnetic filmwill be explained below.

Method for Forming Magnetic Film

The composition of the magnetic film used in this embodiment isTb₁₅Fe₇₅CO₁₀ in which the sub-lattice magnetization of the transitionmetal is dominant. The magnetic film was formed by using the RFmagnetron sputtering method. A Tb—Fe—Co alloy was used for the target,and pure Ar was used for the electric discharge gas. The thickness ofthe formed magnetic film is 20 nm.

During the film formation of the magnetic film, the sputtering wastemporarily interrupted when the film thickness was 5 nm, followed bybeing left to stand as it was for 5 minutes. After that, the filmformation was resumed, and the film formation was temporarilyinterrupted again when the film thickness was 5 nm, followed by beingleft to stand as it was for 5 minutes. The step of forming the film andthe step of being left to stand were repeatedly performed to form thefilm until the film thickness of the magnetic film was a desired filmthickness (about 20 nm). The pressure during the sputtering was 10 mTorr(about 3.99 Pa), and the introduced RF electric power was 1 kW/150 mmφ.The coercivity of the obtained magnetic film was 3.5 kOe (about 278.5kA/m), the saturation magnetization was 250 emu/ml, and theperpendicular magnetic anisotropy energy was 5×10⁶ erg/cm³.

Magnetic characteristics of the magnetic recording medium provided withthe magnetic film as described above were measured. According to an M-Hloop obtained by the measurement with VSM, the rectangularity ratios S,S* were 1.0, and thus good rectangularity was obtained. The coercivityHc was 3.5 kOe (about 278.53 kA/m), and the saturation magnetization Mswas 250 emu/cm³. The perpendicular magnetic anisotropy energy was 5×10⁶erg/cm³. The volume of activation of the magnetic recording medium wasmeasured to determine the value of KuV/kT. As a result, the value was300. This fact indicates that the magnetic film is excellent in thermalstability.

Subsequently, the cross-sectional structure of the magnetic film wasanalyzed by means of the Auger electron spectroscopy. A graph of theresult of the analysis is schematically shown in FIG. 11. According tothe result of the analysis shown in FIG. 11, it is considered that anarea having a high oxygen concentration exists in the magnetic film, andportions having high oxygen concentrations and portions having lowoxygen concentrations (portions containing substantially no oxygen) arealternately present in a layered form. According to this fact, theportions having high oxygen concentrations and the portions having lowoxygen concentrations were successively formed in the magnetic film byforming the film while temporarily interrupting the sputtering when themagnetic film was formed.

Observation with MFM

Subsequently, the magnetic film was subjected to AC (alternate current)demagnetization, and then the surface of the magnetic film was observedwith a magnetic force microscope (MFM). FIG. 12 shows an MFM imageobtained by the observation with MFM. The magnetic film observed in thisembodiment was a magnetic film which was obtained by stopping thesputtering at the point of time at which two layers containing oxygenwere formed in the magnetic film. For the purpose of comparison, FIG. 13shows an MFM image of a surface of a magnetic film formed withoutinterrupting the sputtering operation during the film formation.

In the MFM images shown in FIGS. 12 and 13, the lightness and thedarkness indicate the intensity of the magnification of the magneticfilm. In the respective drawings, it is considered that each of the darkportion (black area) and the light portion (white area) indicates theminimum unit of inversion of magnetization. In the MFM image shown inFIG. 12, the size of each of the dark portion and the light portion inthe lightness and the darkness was extremely small, and the dimensionthereof was about 80 nm in average. According to this fact, it isconsidered that the unit of inversion of magnetization is small in sucha magnetic film, and the minute magnetic domain can be formed therein.On the other hand, in the MFM image shown in FIG. 13, the size of eachof the dark portion and the light portion was large, and the dimensionthereof was not less than 200 nm in average. It is considered to bedifficult to form the minute magnetic domain in such a magnetic film. Asdescribed above, the unit of inversion of magnetization of the magneticfilm can be made small by repeating the step of forming the film and thestep of being left to stand to form the film so that the areas havinghigh oxygen concentrations are formed intermittently in the layered formin the magnetic film when the magnetic film is formed.

Subsequently, a lubricant was applied onto the surface of the magneticdisk based on the use of the magnetic recording medium having themagnetic characteristics as described above, and thus the magnetic diskwas completed. A plurality of magnetic disks were manufactured inaccordance with the same process, and they were coaxially incorporatedinto the magnetic recording apparatus shown in FIGS. 2 and 3 in the samemanner as in the first embodiment. The magnetic recording apparatus asdescribed above was used to record and reproduce information so that therecording and reproduction characteristics of the magnetic disk wereevaluated. During the recording and the reproduction, the distancebetween the magnetic head surface and the magnetic film was maintainedto be 12 nm. A signal (700 kFCI) corresponding to 40 Gbits/inch² wasrecorded on the magnetic disk to evaluate S/N of the disk. As a result,a reproduction output of 34 dB was obtained. On the other hand, in thecase of a magnetic disk manufactured without forming the distribution ofthe oxygen concentration in a magnetic film, the noise was increased byabout 5 dB over the entire frequency area. Thus, the effect to reducethe noise was obtained by forming the areas having the high oxygenconcentrations in the magnetic film as described above.

Subsequently, a definite pattern was recorded on the magnetic disk, andthe fluctuation of the edge of the magnetic domain formed in themagnetic film was measured with a time interval analyzer. As a result ofthe measurement, the fluctuation was successfully reduced to be not morethan {fraction (1/10)} as compared with a magnetic disk having no oxygenconcentration distribution in a magnetic film. Further, the error rateor defect rate of the magnetic disk was measured. As a result, a valueof not more than 1×10⁻⁵ was obtained when no signal processing wasperformed. The magnetization state of the recorded portion was observedwith a magnetic force microscope (MFM). As a result, the zigzag patternpeculiar to the magnetization transition area was not observed. It isconsidered the noise level was successfully reduced thereby.

In this embodiment, the surface of the halfway formed magnetic film wasnaturally oxidized with oxygen as the impurity contained in theatmosphere by temporarily interrupting the film formation when themagnetic film was formed. However, the surface may be positivelyoxidized by allowing the halfway formed magnetic film to be left tostand in an oxygen atmosphere or in an oxygen-containing atmosphereafter the interruption of the film formation. In this procedure, theoxidation of the surface of the magnetic film is further facilitated,and it is possible to further increase the oxygen concentration.Accordingly, it is possible to further reduce the fluctuation of theedge of the magnetic domain formed in the magnetic film.

The magnetic film, which is constructed by alternately stacking thelayers containing oxygen and the layers containing no oxygen, can bealso formed by using a sputtering apparatus of the substrate rotationtype. In the case of the sputtering apparatus of the substrate rotationtype, the substrate holder and the targets are usually arranged as shownin a schematic plan view in FIG. 14. The respective target materials T1to T3 shown in FIG. 14 are target materials, for example, for theunderlying base film, the magnetic film, and the protective film formedon the substrate. When the magnetic film is formed, the target for themagnetic film is subjected to the sputtering while rotating thesubstrate holder at a high velocity so that the magnetic film is formedon the substrate installed to the substrate holder. When the magneticfilm, which is constructed by alternately stacking the layers containingoxygen and the layers containing no oxygen, is formed by using thesputtering apparatus as described above, for example, the number ofrevolutions of the substrate holder may be lowered during the filmformation. When the number of revolutions of the substrate holder islowered, it takes a long period of time to enter an electricallydischarging area (area in which the film is formed) again after passingthrough the area. Therefore, the magnetic film is not formed during aperiod of the location outside the electrically discharging area, andthe surface of the magnetic film is naturally oxidized. In the case ofthe sputtering apparatus as described above, it is unnecessary totemporarily stop the electric discharge when the magnetic film isformed. The magnetic film, which is constructed by alternately stackingthe layers containing oxygen and the layers containing no oxygen, can beformed by only controlling the number of revolutions of the substrateholder.

Thirteenth Embodiment

In this embodiment, an artificial lattice film of Tb/Fe/Co as a magneticfilm was formed in accordance with a method different from that used inthe twelfth embodiment to manufacture a magnetic recording medium havingthe same stacked structure as that shown in FIG. 8. A method for formingthe magnetic film will be explained below.

Method for Forming Magnetic Film

The multi-source co-sputtering method based on three sources of Tb, Fe,and Co was used as the method for forming the magnetic film in the samemanner as in the twelfth embodiment. The film thickness of each of thelayers is Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm). The film thickness of eachof the layers can be precisely controlled to have a desired value bycombining the velocity of revolution of the substrate and the electricpower introduced during the sputtering. In this embodiment, theintroduced DC electric power was 0.3 kW for the formation of the film ofTb, 0.15 kW for the formation of the film of Co, and 0.7 kW for theformation of the film of Fe. The number of revolutions of the substratewas 30 rpm. The electric discharge gas pressure during the sputteringwas 3 mTorr (about 399 mPa). High purity Ar gas was used for theelectric discharge gas. The sputtering operation was temporarilyinterrupted at the point of time at which the Tb layer was formed tonaturally oxidize the surface of the formed Tb layer. The naturaloxidation in this procedure is based on the oxidation with oxygencontained as an impurity in the high purity Ar gas used as the electricdischarge gas. The reason whey the Tb layer was oxidized is that Tbtends to be oxidized most promptly among Fe, Tb, and Co. Thus, theartificial lattice film was formed to have a total thickness of about 40nm by periodically stacking stacked units each composed of Fe (1 nm)/Co(0.1 nm)/Tb (0.2 nm). The magnetic film was observed TEM. As a result,it was revealed that the artificial lattice film composed of Fe (1nm)/Co (0.1 nm)/Tb (0.2 nm) having the desired film thickness wasobtained.

Subsequently, magnetic characteristics of the magnetic recording mediumprovided with the magnetic film as described above were measured.According to an M-H loop measured by the measurement with VSM, both ofthe rectangularity ratios S, S* were 1.0, and thus good rectangularitywas obtained. The coercivity Hc was 3.9 kOe. The perpendicular magneticanisotropy energy in the direction perpendicular to the substratepossessed by the magnetic film was 7×10⁶ erg/cm³. The volume ofactivation of the magnetic recording medium was measured to determinethe value of KuV/kT. As a result, the value of KuV/kT was 400. This factindicates that the magnetic film is formed of a material which isexcellent in thermal stability with small thermal fluctuation and smallthermal demagnetization.

Subsequently, a lubricant was applied onto the surface of the magneticdisk based on the use of the magnetic recording medium having themagnetic characteristics as described above, and thus the magnetic diskwas completed. A plurality of magnetic disks were manufactured inaccordance with the same process, and they were coaxially incorporatedinto the magnetic recording apparatus shown in FIGS. 2 and 3 in the samemanner as in the first embodiment. The magnetic recording apparatus asdescribed above was driven to record and reproduce information so thatthe recording and reproduction characteristics of the magnetic disk wereevaluated. During the recording and the reproduction, the distancebetween the magnetic head surface and the magnetic film was maintainedto be 12 nm. A signal (700 kFCI) corresponding to 40 Gbits/inch² wasrecorded on the magnetic disk to evaluate S/N of the disk. As a result,a reproduction output of 36 dB was obtained. Further, the error rate ordefect rate of the disk was measured. As a result, a value of not morethan 1×10⁻⁵ was obtained when no signal processing was performed.

In this embodiment, the distribution of oxygen was formed in themagnetic film with oxygen or water as the impurity contained in the highpurity Ar gas atmosphere by repeatedly performing the operation fortemporarily interrupting the sputtering in the high purity Ar gasatmosphere (in the residual gas). However, it is also possible to form adistribution of nitrogen in the magnetic film. In this case, it is mostpreferable that the halfway formed magnetic film is naturally nitridedby temporarily interrupting the sputtering operation in anitrogen-containing atmosphere, because the amount of nitrogen in theresidual gas is smaller than those of water and oxygen.

Fourteenth Embodiment

In this embodiment, a magnetic recording medium according to the thirdaspect of the present invention was manufactured. The cross-sectionalstructure of the magnetic recording medium is shown in FIG. 15. In FIG.15, an information-recording film 93 has the structure in whichamorphous alloy films based on the Tb—Co—Fe system and Si films arealternately stacked. A method for producing the magnetic recordingmedium 90 will be explained below.

Preparation of Substrate

At first, a glass substrate having a diameter of about 2.5 inches (about6.35 cm) was prepared as the substrate 91. The substrate used in thisembodiment is an example. A disk substrate having any size may be used,and a metal substrate such as Al or Al alloy may be used. The effect ofthe present invention is not affected by the material quality and thesize of the substrate to be used. Further, it is also allowable to use asubstrate comprising an NiP layer formed on a substrate of glass, Al, orAl alloy by means of the plating method or the sputtering method.

Formation of Underlying Base Film

Subsequently, a silicon nitride film was formed as the underlying basefilm 92 having a film thickness of 50 nm on the substrate 91 by means ofthe RF magnetron sputtering method. Silicon was used for the targetmaterial, and an Ar—N₂ mixed gas (Ar/N₂ partial pressure ratio: 90/10)was used for the electric discharge gas. The pressure during thesputtering was 3 mTorr (about 399 mPa), and the introduced RF electricpower was 1 kW/150 mmφ. The sputtering was performed at the roomtemperature.

The underlying base film 92 makes it possible to improve the adhesiveperformance between the substrate 91 and the information-recording film93, it has the function as the nucleation site when a magnetic field isapplied from the outside to the information-recording film 93 to formthe magnetic domain, and it has the effect as the obstacle for themagnetic wall movement. Such an effect not only depends on the materialfor constructing the underlying base film 92 but also depends on thecondition for the film formation. The material for the underlying basefilm 9.2 is not limited to silicon nitride as well. It is also allowableto use a metal film such as Ni—P, Al, Al—Cr alloy, Cr, and Cr—Ti alloy.Alternatively it is also allowable to use an inorganic compound such asAlN, ZrO₂, and BN.

Formation of Information-Recording Film

Subsequently, a film constructed by alternately stacking amorphous alloyfilms based on the Tb—Fe—Co system and Si films was formed as theinformation-recording film 93 on the underlying base film 92 withoutbreaking the vacuum after the formation of the underlying base film 92.The composition of the amorphous alloy film based on the Tb—Fe—Co systemfor constructing the information-recording film 93 is Tb₁₅Fe₇₅Co₁₀ inwhich the sub-lattice magnetization of the transition metal is dominant.The RF magnetron sputtering method was used for the formation of theinformation-recording film 93. In the sputtering for the amorphous alloyfilm based on the Tb—Fe—Co system, a Tb—Fe—Co alloy was used for thetarget material, and pure Ar was used for the electric discharge gas. Inthe sputtering for the Si film, Si was used for the target material, andpure Ar was used for the electric discharge gas.

When the information-recording film 93 was formed, the operation, inwhich Tb—Fe—Co was formed to have a film thickness of 5 nm and then theSi film was formed to have a film thickness of 0.2 nm, was repeatedlyperformed to alternately stack the Tb—Fe—Co films and the Si films. Thefilm formation was performed until the film thickness of the Tb—Fe—Cofilms was 20 nm in total. The electric discharge gas pressure during thesputtering was 10 mTorr (about 1.33 Pa), and the introduced RF electricpower was 1 kW/150 mmφ.

The coercivity of the obtained information-recording film 93 was 3.5 kOe(about 278.53 kA/m), the saturation magnetization was 250 emu/ml, andthe perpendicular magnetic anisotropy energy was 5×10⁶ erg/cm³.

Formation of Protective Film

Finally, a C (carbon) film was formed to have a film thickness of 5 nmas the protective film 94 on the information-recording film 93 by meansof the ECR sputtering method. C was used for the target material, and Arwas used for the electric discharge gas. The pressure during thesputtering was 0.3 mTorr, and the introduced microwave electric powerwas 0.7 kW. An RF bias voltage of 500 W was applied in order to draw theplasma excited by the microwave. The hardness of the manufacturedprotective film 94 was measured with a hardness tester produced byHysitron. As a result, the hardness was 21 GPa. According to a resultobtained by the Raman spectroscopy, it was revealed that the sp3 bondplayed a key role.

When the protective film 94 was formed, Ar was used for the sputteringgas. However, the film may be formed with a gas containing nitrogen.When the gas containing nitrogen is used, then the grains become fineand minute, the obtained C film is densified, and it is possible tofurther improve the protective performance. As described above, the filmquality of the protective film greatly depends on the sputteringcondition and the electrode structure. Therefore, the conditionsdescribed above are not absolute. It is desirable that the conditionsare appropriately adjusted depending on the apparatus to be used.

Measurement of Magnetic Characteristics

Thus, the magnetic recording medium 90 having the stacked structureshown in FIG. 15 was manufactured, and magnetic characteristics of theobtained magnetic recording medium 90 were measured. An M-H loop wasobtained by the measurement with VSM. According to the obtained results,the rectangularity ratios S, S* were 1.0. It was revealed that goodrectangularity was obtained. The coercivity Hc was 3.5 kOe (about 278.53kA/m), and the saturation magnetization Ms was 250 emu/cm³. Theperpendicular magnetic anisotropy energy in the direction perpendicularto the substrate surface was 5×10⁶ erg/cm³. The volume of activation ofthe information-recording film of the magnetic recording medium wasmeasured to determine the value of KuV/kT. As a result, the value was300. This fact indicates that the information-recording film of themagnetic recording medium is excellent in thermal stability.

Subsequently, the cross-sectional structure of the information-recordingfilm of the magnetic recording medium was observed with a transmissionelectron microscope (TEM). FIG. 16 schematically shows an observedsituation. As a result of the observation, it is appreciated that the Sifilms 96 and the Tb—Fe—Co films 95 are alternately stacked. It was alsorevealed from the TEM observation that the Tb—Fe—Co film was amorphous.

Magnetic Recording Apparatus

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium, and thus the magnetic disk was completed. A pluralityof magnetic disks were manufactured in accordance with the same process,and they were coaxially incorporated into the magnetic recordingapparatus shown in FIGS. 2 and 3 in the same manner as in the firstembodiment. The magnetic recording apparatus as described above was usedto record and reproduce information so that recording and reproductioncharacteristics of the magnetic disk were evaluated. The distancebetween the magnetic head surface and the magnetic film was maintainedto be 12 nm during the recording and the reproduction. A signal (700kFCI) corresponding to 40 Gbits/inch² (about 6.20 Gbits/cm²) wasrecorded on the magnetic disk to evaluate S/N of the magnetic disk. As aresult, a reproduction output of 34 dB was obtained. The signal wasrecorded in the same manner as described above on a magnetic recordingmedium including an information-recording film constructed with only anamorphous alloy film based on the Tb—Fe—Co system to evaluate S/N. As aresult, the noise was increased by about 5 dB over the entire frequencyarea.

Subsequently, a definite pattern was recorded on the magnetic disk ofthe present invention, and the fluctuation of the edge of the magneticdomain formed in the information-recording film was measured with a timeinterval analyzer. As a result of the measurement, the fluctuation wassuccessfully reduced to be not more than {fraction (1/10)} as comparedwith a conventional magnetic disk including an information-recordingfilm composed of only an amorphous alloy film based on the Tb—Fe—Cosystem. Further, the error rate or defect rate of the magnetic disk wasmeasured. As a result, a value of not more than 1×10⁻⁵ was obtained whenno signal processing was performed. The magnetization state of therecorded portion was observed with a magnetic force microscope (MFM). Asa result, the zigzag pattern peculiar to the magnetization transitionarea was not observed. It is considered the noise level was successfullyreduced thereby.

In this embodiment, Si was used as the material for the non-magneticfilm for constructing the information-recording film. However, the sameor equivalent effect can be also obtained, for example, even whenanother element such as Cr, Nb, Ti, Ta, Al, Pd, Rh, Zr, Re, Mo, W, Ir,V, or Cu is used in place of Si. The corrosion resistance of theinformation-recording film was successfully improved by using such thematerial as described above, for the following reason. That is, thenon-magnetic film, which is stacked alternately with respect to themagnetic film, can suppress the diffusion of oxygen contained asimpurity in the magnetic film.

In this embodiment, the amorphous ferrimagnetic film based on theTb—Fe—Co system was used for the magnetic film for constructing theinformation-recording film. However, the same or equivalent effect wasalso obtained, for example, even when Dy, Ho, or Gd was used in place ofTb. Among these elements, the largest perpendicular magnetic anisotropyis obtained with Tb. The magnitude of the perpendicular magneticanisotropy is changed in an order of Dy>Ho>Gd. A plurality of rare earthelements may be used in combination, i.e., for example, alloys composedof two elements such as Tb—Gd, Tb—Dy, Tb—Ho, Gd—Dy, Gd—Ho, and Dy—Ho andalloys composed of three or more elements, in place of the constructionof the rare earth element for constructing the magnetic film with onlyTb. Accordingly, it is possible to control the perpendicular magneticanisotropy energy. It is preferable that the composition of the rareearth element is not less than 20 at % and not more than 30 at % to formthe perpendicularly magnetizable film, for the following reason. Thatis, when such a range is adopted, it is possible to obtain aferrimagnetic member having an easy axis of magnetization in thedirection perpendicular to the substrate surface.

The F—Co alloy was used as the transition metal. However, it is alsoallowable to use alloys such as Fe—Ni and Co—Ni. As for such alloys, theanisotropy energy is decreased in an order of Fe—Co>Fe—Ni>Co—Ni.

Fifteenth Embodiment

In this embodiment, a magnetic recording medium having the same stackedstructure as that of the magnetic recording medium manufactured in thefourteenth embodiment (see FIG. 15) was manufactured except that anartificial lattice film of Tb/Fe/Co was used in place of the amorphousalloy film based on the Tb—Fe—Co system as the magnetic film forconstructing the information-recording film, and an Nb film was used inplace of the Si film. The method for forming those other than theinformation-recording film is the same as that used in the fourteenthembodiment, explanation of which is omitted. A method for forming theinformation-recording film having the structure constructed byalternately stacking the Tb/Fe/Co artificial lattice films and the Nbfilms will be explained below.

Method for Forming Information-Recording Film

When the Tb/Fe/Co artificial lattice film in the information-recordingfilm was formed, the DC multi-source co-sputtering method based on threesources of Tb, Fe, and Co was used. The film thickness of each of thelayers is Fe (1 nm)/Co (0.1 nM)/Tb (0.2 nm). The film thickness of eachof the layers can be precisely controlled to have a desired value bycombining the velocity of revolution of the substrate and the electricpower introduced during the sputtering. In this embodiment, theintroduced DC electric power was set to be 0.3 kW for forming the layerof Tb, 0.15 kW for forming the layer of Co, and 0.7 kW for forming thelayer of Fe. The number of revolutions of the substrate was 30 rpm. Theelectric discharge gas pressure during the sputtering was 3 mTorr, andhigh purity Ar gas was used for the electric discharge gas. When the Nbfilm was formed, the DC sputtering method was used. The electricdischarge gas pressure during the sputtering was 3 mTorr (about 399mPa), the number of revolutions of the substrate was 30 rpm, and theintroduced DC electric power was 0.7 kW. Nb was used for the target, andpure Ar was used for the electric discharge gas.

When the information-recording film was formed, then the artificiallattice film of Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm) was formed to have afilm thickness of about 4 nm, and then the Nb film was formed to have afilm thickness of about 0.3 nm. The film was formed until the entirefilm thickness of the artificial lattice film was 20 nm by repeatedlyperforming the formation of the Tb/Fe/Co artificial lattice film and theformation of the Nb film. The Nb film, which is formed on the Tb/Fe/Coartificial lattice film, covers the film surface of the Tb/Fe/Coartificial lattice film in an island form as viewed in a plan view. Thesame or equivalent effect is also obtained even when Nb as anon-magnetic element is dispersed in the Fe layer of the Tb/Fe/Coartificial lattice film to construct the film, in place of theconstruction by alternately stacking the Tb/Fe/Co artificial latticefilm and the Nb film.

When the Tb/Fe/Co artificial lattice film as described above ismanufactured, the degree of vacuum at the initial evacuation isimportant. In this embodiment, the film was manufactured after effectingthe evacuation up to 4×10⁻⁹ Torr. The values as described above are notabsolute, which change depending on, for example, the system of thesputtering. In this embodiment, the film was manufactured by means ofthe DC magnetron sputtering method. However, the film formation may becarried out by using the RF magnetron sputtering method and thesputtering method (ECR sputtering method) based on the use of theelectron cyclotron resonance.

When the artificial lattice film as described above is used for themagnetic film in the information-recording film, then it is possible toincrease the perpendicular magnetic anisotropy energy as compared with acase in which an amorphous alloy film based on the Tb—Fe—Co system isused, and it is possible to improve the thermal stability. Theartificial lattice film exhibits substantially the same magneticcharacteristics as those of a ferrimagnetic member composed of atransition metal such as Fe and Co and a rare earth element such as Tb.The magnetization of such an artificial lattice film appears as thedifference between the magnetization of the transition metal thin filmlayer and the magnetization of the rare earth element thin film layer.The artificial lattice film manufactured in this embodiment is anartificial lattice film in which the magnetization of the transitionmetal is dominant.

Measurement of Magnetic Characteristics

Subsequently, magnetic characteristics of the magnetic recording mediumprovided with the information-recording film composed of the Tb/Fe/Coartificial lattice film and the Nb film were measured. An M-H loop wasobtained by the measurement with VSM (Vibration Sample Magnetometer).According to the obtained results, both of the rectangularity ratios S,S* were 1.0. It was revealed that good rectangularity was obtained. Thecoercivity Hc was 3.9 kOe (about 310.362 kA/m). As for the magneticanisotropy energy of the magnetic film, the perpendicular magneticanisotropy energy in the direction perpendicular to the substratesurface was 1×10⁷ erg/cm³. The volume of activation V of the magneticrecording medium was measured to determine the value of KuV/kT as theindex for the thermal stability of the information-recording film. As aresult, the value of KuV/kT was 400. This fact indicates that theinformation-recording film is formed of a material which is excellent inthermal stability with small thermal fluctuation and small thermaldemagnetization.

Further, the cross-sectional structure of the information-recording filmwas observed with a high resolution transmission electron microscope(high resolution TEM). As a result, it was revealed that theinformation-recording film had the structure in which the artificiallattice film of Fe (1 nm)/Co (0.1 nm)/Tb (0.2 nm) and the Nb film wereperiodically stacked with the desired film thickness.

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium, and thus the magnetic disk was completed. A pluralityof magnetic disks were manufactured in accordance with the same process,and they were coaxially incorporated into the magnetic recordingapparatus shown in FIGS. 2 and 3 in the same manner as in the firstembodiment. The magnetic recording apparatus as described above was usedto record and reproduce information. During the recording and thereproduction, the distance between the magnetic head surface and theinformation-recording film was maintained to be 12 nm. A signal (700kFCI) corresponding to 40 Gbits/inch² (about 6.20 Gbits/cm²) wasrecorded on the magnetic disk to evaluate S/N of the disk. As a result,a reproduction output of 36 dB was obtained. The error rate or defectrate of the magnetic disk was measured. As a result, a value of not morethan 1×10 ⁻⁵ was obtained when no signal processing was performed.

This embodiment is illustrative of the case in which the artificiallattice film based on the Tb/Fe/Co system is used. However, the same orequivalent effect is obtained even when one element of Gd, Dy, and Ho isused other than Tb, or even when an alloy such as Gd—Tb, Gd—Dy, Gd—Ho,Tb—Dy, and Tb—Ho is used. The artificial lattice film was constructed byusing the two-layered film of Fe/Co as the transition metal. However, itis also possible to obtain a magnetic film having equivalentcharacteristics by using an alternately stacked multilayered filmcomposed of an alloy such as Fe—Co, Fe—Ni, and Co—Ni and a rare earthelement such as Tb.

Sixteenth Embodiment

In this embodiment, three types of magnetic recording media wereproduced in the same manner as in the fifteenth embodiment except thatthe electric discharge gas pressure, which was used when theinformation-recording film was formed, was changed to have threedifferent values, i.e., 5 mTorr (about 665 mPa), 10 mTorr (about 1.33Pa), and 20 mTorr (about 2.66 Pa). The coercivities of theinformation-recording films of the respective magnetic recording mediawere measured. As a result, any one of them was 3.9 kOe (about 308.1kA/m).

δM Plot

The δM plot was obtained for the obtained three types of magneticrecording media. A method for measuring the δM plot will be explainedbelow. At first, the M-H curve of the information-recording film of themagnetic recording medium was determined with VSM. The remanence(remanent magnetization) was determined from the obtained M-H curve.Subsequently, the DC (direct current) demagnetization remanentmagnetization curve Id(H) (DC demagnetization remanence curve) and theisothermal remanent magnetization curve Ir(H) (isothermal remanencemagnetization curve) were determined. The following calculation was madewith the obtained Id(H) and Ir(H):δM(H)=Id(H)−[1−2Ir(H)]The value of δM(H) was plotted with respect to the applied magneticfield H.

Obtained δM plot curves are shown in FIG. 17. According to the δM plotcurves shown in FIG. 17, the following fact was revealed for themagnetic recording medium for which the information-recording film wasmanufactured with the electric discharge gas pressure of 20 mTorr. Thatis, δM(H) remained zero without depending on the magnetic fieldintensity H, and no peak was observed on the δM plot curve. On the otherhand, in the case of the magnetic recording media having theinformation-recording films formed at the electric discharge gaspressures of 10 mTorr and 5 mTorr, peaks were obtained on the δM plotcurves at 800 Oe (about 63.66 kA/m) and 2.4 kOe (about 190.99 kA/m).According to this fact, it is appreciated that the strong exchangecoupling force is exerted on the information-recording film in each ofthe magnetic recording-media having the information-recording filmsformed at the electric discharge gas pressures of 10 mTorr and 5 mTorr.According to the results as described above, it has been revealed thatthe exchange coupling can be remarkably lowered when theinformation-recording film is formed at a high electric discharge gaspressure, probably for the following reason. That is, when the gaspressure during the sputtering is high, then the sputtering particlesare clustered, and the bulk density of the information-recording film islowered.

Besides the information-recording film is formed by changing theelectric discharge gas pressure, the peak position on the δM plot curvecan be also controlled even when the film thickness of the Nb layerformed in the information-recording film is changed. However, if thetotal film thickness of the Nb layer for constructing theinformation-recording film is not less than 2 nm, the magnetizationexhibited by the information-recording film suddenly disappears. Thisfact indicates that any optimum film thickness is present for the Nbfilm in the information-recording film. Alternatively, Nb may be addedas an alloy to the Fe layer, Co layer, and the layer of the rare earthelement, in place of the formation of Nb in the layered form in theinformation-recording film. The decrease in exchange coupling forcecaused by the film formation at a high electric discharge gas pressureis not necessarily caused in only the film formation of theinformation-recording film constructed by alternately stacking themagnetic films and the non-magnetic films. For example, even when anamorphous alloy film (for example, a Tb—Fe—Co amorphous alloy film),which is composed of a single layer, is formed at a high electricdischarge gas pressure, then the peak position on the δM plot curve forthe amorphous alloy film can be deviated toward the low magnetic fieldside, or the peak is successfully allowed to disappear. Accordingly, theexchange coupling force of the amorphous alloy film can be lowered.

Subsequently, a lubricant was applied onto the surface of the magneticrecording medium having the information-recording film formed at theelectric discharge gas pressure of 20 mTorr, and thus the magnetic diskwas completed. A plurality of magnetic disks were manufactured inaccordance with the same process, and they were coaxially incorporatedinto the magnetic recording apparatus shown in FIGS. 2 and 3 in the samemanner as in the first embodiment. The magnetic recording apparatus asdescribed above was used to record and reproduce information. During therecording and the reproduction, the distance between the magnetic headsurface and the information-recording film was maintained to be 12 nm. Asignal (800 kFCI) corresponding to 50 Gbits/inch² was recorded on themagnetic disk to evaluate S/N of the disk. As a result, a reproductionoutput of 36 dB was obtained. The error rate or defect rate of themagnetic disk was measured. As a result, a value of not more than 1×10⁻⁵was obtained when no signal processing was performed.

The magnetic recording medium according to the present invention and themagnetic recording apparatus provided with the same have been explainedwith reference to the embodiments described above. However, the presentinvention is not limited thereto, which may include a variety ofimproved embodiments and modified embodiments.

For example, a Pt—Co alloy film may be formed on theinformation-recording film in order to improve S/N of the magneticrecording medium manufactured in each of the tenth to fifteenthembodiments. When the Pt—Co alloy film is formed, for example, thetwo-source co-sputtering method based on two source targets of Pt and Cocan be used. It is also allowable to use the RF magnetron sputteringmethod, the DC magnetron sputtering method, and the ECR sputteringmethod based on the use of the resonance absorption method, other thanthe two-source co-sputtering method.

In the tenth to sixteenth embodiments, the magnetic recording medium ofthe perpendicular magnetic recording type was produced by constructingthe information-recording film (or the magnetic film) by using theperpendicularly magnetizable film having the easy axis of magnetizationin the direction perpendicular to the substrate surface. However, amagnetic recording medium of the in-plane magnetic recording type can bealso constructed by using the in-plane magnetizable film used for theinformation-recording film of the magnetic recording medium as describedin each of the eighth and ninth embodiments.

The stacked structure of the magnetic recording medium is not limited tothose described in the embodiments. For example, it is also possible toform a soft magnetic film composed of a soft magnetic material. Such asoft magnetic film is preferably formed so that theinformation-recording film intervenes between the soft magnetic film andthe magnetic head. It is desirable that the soft magnetic film is formedwithout making contact with the layer having magnetization of the layersfor constructing the magnetic recording medium. For example, in the caseof the first to seventh embodiments described above, it is desirablethat the soft magnetic film is formed without making contact with theinformation-recording film, the ferromagnetic film, and the first tothird magnetic films with the nonmagnetic layer interveningtherebetween. Accordingly, a magnetic circuit is formed between themagnetic head and the soft magnetic film during the recording ofinformation, and the magnetic field is applied from the magnetic head tothe magnetic recording film in only the direction perpendicular to thefilm surface. Further, the magnetic coupling is generated between themagnetic head and the soft magnetic film. Therefore, the magnetic fieldfrom the magnetic head is applied to only a narrow area of theinformation-recording film at a large magnetic field intensity.Therefore, it is possible to form fine and minute recording magneticdomains in the magnetic recording film. Those usable for the softmagnetic film as described above include, for example, magneticmaterials such as NiFe, Fe—Ta—C, Fe—Hf—N, Al—Si—Fe, Gd—Fe, and Gd—Fe—Co.

Details of the structure of the magnetic recording apparatus (hard diskapparatus) are disclosed in U.S. Pat. No. 5,851,643. The contents ofthis document are incorporated herein by reference within a range ofpermission of the domestic laws and ordinances of the designated stateor the selected state.

INDUSTRIAL APPLICABILITY

The magnetic recording medium according to the first aspect of thepresent invention comprises, as the information-recording film, theamorphous magnetic film which has the large volume of activation andwhich is excellent in thermal stability with small thermaldemagnetization and small thermal fluctuation. Therefore, the magneticrecording medium according to the first aspect of the present inventionis extremely suitable as the magnetic recording medium for the highdensity recording. Further, the magnetic recording medium according tothe first aspect of the present invention is provided with theferromagnetic film having the saturation magnetization larger than thatof the amorphous magnetic film. Therefore, even when minute magneticdomains are formed in the amorphous magnetic film, then the amplifiedreproduced signal output can be obtained from the ferromagnetic film,and information can be reliably reproduced. Further, the amorphousmagnetic film has the amorphous structure. Therefore, it is unnecessaryto form any seed layer for controlling the crystalline orientation ofthe magnetic film. It is possible to simplify the stacked structure ofthe magnetic recording medium. Therefore, the magnetic recording mediumof the present invention can be mass-produced in a large amount at a lowprice.

When the amorphous magnetic film is constructed with the artificiallattice film having the easy axis of magnetization in the directionperpendicular to the substrate surface, it is possible to provide themagnetic recording medium which has the larger magnetic anisotropy andwhich is excellent in thermal stability.

Further, the magnetic recording medium according to the first aspect ofthe present invention may comprise the magnetic wall movement controllayer for suppressing the movement of the magnetic wall of the amorphousmagnetic film of the magnetic wall movement type. Accordingly, theminute recording magnetic domain can be formed to have the desired edgeshape in the amorphous magnetic film, and the edge position can bepositioned highly accurately. Therefore, it is possible to reduce thefluctuation of the recording magnetic domain formed in the amorphousmagnetic film, and it is possible to reliably reproduce informationsubjected to the high density recording.

In the magnetic recording medium according to the second aspect of thepresent invention, the pinning sites are formed in the dispersed mannerin the magnetic film by containing the significant amount of at leastone of oxygen and nitrogen in the magnetic film of the magnetic wallmovement type such as the amorphous film. Therefore, the magnetic wallin the magnetic film is prevented from movement, and it is possible toform the recording magnetic domain highly accurately at the desiredposition in the magnetic film.

Even in the case of the minute recording magnetic domain, the edge ofthe magnetic domain can be formed to have the desired shape, and theedge position can be positioned highly accurately. Therefore, it ispossible to reduce the fluctuation of the recording magnetic domain.Therefore, it is possible to record information at the super highdensity, and it is possible to reliably reproduce information subjectedto the high density recording.

When the magnetic film is constructed with the ferrimagnetic materialcomposed of the rare earth element-iron family element, it is possibleto provide the magnetic recording medium which is excellent in thermalstability with small thermal demagnetization and small thermalfluctuation.

According to the production methods of the third and fourth aspects ofthe present invention, at least one of oxygen and nitrogen can becontained at the desired concentration in the magnetic film. Therefore,the production methods according to the third and fourth aspects of thepresent invention are extremely suitable as the method for producing themagnetic recording medium according to the second aspect of the presentinvention.

The magnetic recording medium according to the fifth aspect of thepresent invention comprises the information-recording film having thestructure constructed by alternately stacking the magnetic filmscomposed of the magnetic material and the non-magnetic films composed ofthe non-magnetic material having the film thickness of not more than 1nm. The non-magnetic film is subjected to the dispersion in the islandform in the film surface. Such an island-shaped non-magnetic filmfunctions as the pinning site. Therefore, the magnetic wall in theinformation-recording film is prevented from movement. The recordingmagnetic domain formed in the information-recording film can bepositioned highly accurately, and the position can be maintained in thestable manner.

Even in the case of the minute recording magnetic domain, the edge shapeof the magnetic domain can be formed to be the desired shape. Further,the edge position can be positioned highly accurately. Therefore, it ispossible to reduce the fluctuation of the recording magnetic domain.Therefore, it is possible to record information at the super highdensity, and it is possible to reliably reproduce information subjectedto the high density recording. The magnetic recording apparatusaccording to the present invention makes it possible to reliably recordinformation on the magnetic recording medium having the high coercivity.Therefore, the magnetic recording apparatus according to the presentinvention is extremely suitable as the next-generation magneticrecording apparatus for the super high density recording. It is possibleto realize the areal recording density exceeding 40 Gbits/inch² (6.20Gbits/cm²).

1. A magnetic recording medium for reproducing information thereon witha magnetic head, the magnetic recording medium comprising: a substrate;an amorphous magnetic film which has an easy axis of magnetization in adirection perpendicular to a substrate surface and in which informationis recorded; and a ferromagnetic film; wherein: the ferromagnetic filmhas an easy axis of magnetization in the direction perpendicular to thesubstrate surface, the ferromagnetic film has saturation magnetizationlarger than saturation magnetization of the amorphous magnetic film, theferromagnetic film contacts with the amorphous magnetic film, and theferromagnetic film is formed on a side closer to the magnetic head thanthe amorphous magnetic film; and wherein the amorphous magnetic film hasa single layer film or an artificial lattice film, and is composed of analloy comprising an iron family element and a rare earth element, theiron family element is at least one element selected from the groupconsisting of Fe, Co, and Ni, and the rare earth element is at least oneelement selected from the group consisting of Th, Gd, Dy, and Ho.
 2. Themagnetic recording medium according to claim 1, wherein the sub-latticemagnetization of the ferrimagnetic material is rich in iron familyelements.
 3. The magnetic recording medium according to claim 1, whereinthe amorphous magnetic film is an artificial lattice film, and theartificial lattice film has a structure in which one or more layerscomposed of an iron family element and one or more layers composed of arare earth element are alternately stacked.
 4. The magnetic recordingmedium according to claim 3, wherein the iron family element is at leastone element selected from the group consisting of Fe, Co, and Ni, andthe rare earth element is at least one element selected from the groupconsisting of Tb, Gd, Dy, and Ho.
 5. The magnetic recording mediumaccording to claim 3, wherein the layer composed of the iron familyelement includes a plurality of layers, and the plurality of layers havetwo layers which are composed of at least two elements selected from thegroup consisting of Fe, Co, and Ni.
 6. The magnetic recording mediumaccording to claim 3, wherein the layer composed of the iron familyelement is a thin film which is composed of an alloy comprising at leasttwo elements selected from the group consisting of Fe, Co, and Ni. 7.The magnetic recording medium according to claim 1, wherein theferromagnetic film is a layer which increases a magnetic flux generatedfrom the amorphous magnetic film.
 8. The magnetic recording mediumaccording to claim 1, further comprising a magnetic wall movementcontrol layer which suppress movement of a magnetic wall formed in theamorphous magnetic film.
 9. The magnetic recording medium according toclaim 8, wherein the magnetic wall movement control layer is composed ofa magnetization rotation type magnetic material.
 10. The magneticrecording medium according to claim 9, wherein the magnetic wallmovement control layer is composed of an alloy which principallycontains any one of materials of Co, partial oxidation product of Co,and Co—Cr alloy and which further contains at least one element selectedfrom the group consisting of Pt, Pd, Ta, Nb, and Ti.
 11. The magneticrecording medium according to claim 9, wherein the amorphous magneticfilm, the ferromagnetic film, and the magnetic wall movement controllayer have the same direction of easy axis of magnetization.
 12. Themagnetic recording medium according to claim 9, wherein a coercivity ofthe amorphous magnetic film is largest among coercivities of theamorphous magnetic film, the ferromagnetic film, and the magnetic wallmovement control layer.
 13. The magnetic recording medium according toclaim 9, wherein saturation magnetization of the ferromagnetic film islargest among saturation magnetizations of the amorphous magnetic film,the ferromagnetic film, and the magnetic wall movement control layer.14. The magnetic recording medium according to claim 9, wherein theamorphous magnetic film, the ferromagnetic film, and the magnetic wallmovement control layer are stacked so that the amorphous magnetic filmis positioned between the ferromagnetic film and the magnetic wallmovement control layer, the ferromagnetic film is positioned on a sideclose to the magnetic head, and the magnetic wall movement control layeris positioned on a side far from the magnetic head.
 15. The magneticrecording medium according to claim 1, wherein perpendicular magneticanisotropy energy in a direction perpendicular to a substrate surface ofthe amorphous magnetic film is not less than 5×10⁶ erg/cm³.
 16. Themagnetic recording medium according to claim 1, wherein a magneticdomain is formed as recording information in the amorphous magneticfilm, thermal stability of the amorphous magnetic film is represented byKuV/kT provided that Ku represents a magnetic anisotropy constant, Vrepresents a volume of activation, k represents the Boltzmann'sconstant, and T represents a temperature, and the volume of activation Vin the amorphous magnetic film is substantially equal to a volume of onemagnetic domain formed in the amorphous magnetic film.
 17. The magneticrecording medium according to claim 1, wherein the amorphous magneticfilm has saturation magnetization of not less than 100 emu/cm³, acoercivity of not less than 3 kOe, and a film thickness of not more than100 nm.
 18. The magnetic recording medium according to claim 7, whereinthe ferromagnetic film is composed of a magnetic thin film principallycontaining a mixture of Co and oxide of Co or an alloy principallycontaining Co.
 19. The magnetic recording medium according to claim 18,wherein the ferromagnetic film further contains at least one elementselected from the group consisting of Cr, Pt, Pd, Ta, Nb, Si, and Ti.20. The magnetic recording medium according to claim 7, wherein theferromagnetic film is an alternately stacked multilayered film in whichone or more layers composed of at least one element selected from thegroup consisting of Co, Ni, and Fe and one or more layers composed of atleast one element selected from the group consisting of Pt, Pd, and Rhare alternately stacked.
 21. The magnetic recording medium according toclaim 7, wherein the ferromagnetic film is an alternately stackedmultilayered film in which one or more alloy layers composed of at leastone element selected from the group consisting of Co, Ni, and Fe and atleast one element selected from the group consisting of Pt, Pd, and Rh,and one or more layers composed of at least one element selected fromthe group consisting of Pt, Pd, and Rh are alternately stacked.
 22. Themagnetic recording medium according to claim 1, wherein substantially nopeak is present, or a magnetic field intensity to form a peak is notmore than 30% of a coercivity of the amorphous magnetic film in a curverepresented by δM(H) represented by the following expression:δM(H)=Id(H)−[1−2Ir(H)] provided that functions to represent isothermalremanent magnetization and DC demagnetization remanent magnetizationwith respect to an external magnetic field H for the amorphous magneticfilm are Ir(H) and Id(H) respectively.
 23. The magnetic recording mediumaccording to claim 1, wherein the substrate is formed with a materialselected from the group consisting of glass, resin, and Al alloy. 24.The magnetic recording medium according to claim 1, wherein aconvex/concave texture is provided on a substrate surface.
 25. Themagnetic recording medium according to claim 24, wherein movement of amagnetic wall of a recording magnetic domain is suppressed by thetexture during recording of information.
 26. The magnetic recordingmedium according to claim 1, further comprising a protective layer whichis composed of carbon.
 27. A magnetic recording apparatus comprising:the magnetic recording medium as defined in claim 1; a magnetic headwhich records or reproduces information; and a drive unit which drivesthe magnetic recording medium.
 28. The magnetic recording apparatusaccording to claim 27, wherein a magnetic domain having a constant widthand a constant length is formed in the recording medium with themagnetic head to record information.
 29. The magnetic recordingapparatus according to claim 27, wherein the magnetic head comprises anelement which has a resistance that is changeable depending on a changeof magnetic flux, and information is reproduced with the element. 30.The magnetic recording apparatus according to claim 27, furthercomprising an optical head which radiates a light beam onto the magneticrecording medium.
 31. The magnetic recording apparatus according toclaim 30, wherein information is recorded or erased by applying amagnetic field with the magnetic head while radiating the light beamonto the magnetic recording medium with the optical head so that themagnetic recording medium is heated during recording of information. 32.The magnetic recording apparatus according to claim 31, wherein theoptical head radiates a pulsed light beam onto the magnetic recordingmedium.
 33. The magnetic recording apparatus according to claim 32,wherein the pulsed light beam has a form of multipulse composed ofpulses each having a constant width.
 34. The magnetic recordingapparatus according to claim 32, wherein the magnetic head applies, tothe magnetic recording medium, a pulsed magnetic field which issynchronized with the pulsed light beam.
 35. The magnetic recordingapparatus according to claim 34, wherein the magnetic recordingfrequency of not less than 50 MHz.
 36. The magnetic recording apparatusaccording to claim 27, wherein the recording is preformed so that awidth in a track direction of a recording magnetic domain formed on atrack of the magnetic recording medium is narrower than a gap width ofthe magnetic head.
 37. The magnetic recording apparatus according toclaim 28, wherein an areal recording density above 40 Gbits/inch² isprovided.